MainActivity
import android.content.DialogInterface;
import android.content.Intent;
import android.graphics.Typeface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.HashMap;
import java.util.Map;

public class MainActivity extends AppCompatActivity {
    Button login_button;
    EditText Username,Password;
    String username,password;
    String login_url = "http://IP_ADDRS/VolleyAndroid/login.php";
    AlertDialog.Builder builder;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        builder = new AlertDialog.Builder(MainActivity.this);
        login_button = (Button)findViewById(R.id.login_btn);
        Username = (EditText)findViewById(R.id.emailln);
        Password = (EditText)findViewById(R.id.passln);
        login_button.setOnClickListener(new View.OnClickListener(){

            @Override
            public void onClick(View v){
                username = Username.getText().toString();
                password = Password.getText().toString();

                if(username.equals("") || password.equals("")){
                    builder.setTitle("Something Went wrong");
                    displayAlert("Enter a valid username and password");
                }
                else{
                    StringRequest stringRequest = new StringRequest(Request.Method.POST, login_url,
                    new Response.Listener<String>(){
                        @Override
                        public void onResponse(String response){

                            try {
                                JSONArray jsonArray = new JSONArray(response);
                                JSONObject jsonObject = jsonArray.getJSONObject(0);
                                String code = jsonObject.getString("code");
                                if(code.equals("login_failed")){
                                    builder.setTitle("Login Error");
                                    displayAlert(jsonObject.getString("message"));
                                }
                                else{
                                    Intent intent = new Intent (MainActivity.this,LoginSuccess.class);
                                    Bundle bundle = new Bundle();
                                    bundle.putString("name",jsonObject.getString("name"));
                                    bundle.putString("email",jsonObject.getString("email"));
                                    intent.putExtras(bundle);
                                    startActivity(intent);

                                }

                            } catch (JSONException e) {
                                e.printStackTrace();
                            }

                        }
                    }, new Response.ErrorListener(){
                        @Override
                        public void onErrorResponse(VolleyError error){

                        }

                    })
                    {
                        @Override
                        protected Map<String, String> getParams() throws AuthFailureError {
                        Map<String,String> params = new HashMap<String, String>();
                        params.put("user_name",username);
                        params.put("password",password);
                        return params;
                    }
                    };
                    MySingleton.getInstance(MainActivity.this).addToRequest(stringRequest);
                }
            }
        });

    }

    public void displayAlert(String message){
        builder.setMessage(message);
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                Username.setText("");
                Password.setText("");
            }
        });

        AlertDialog alertDialog = builder.create();
        alertDialog.show();
    }

    public void register(View v){
        Intent intent = new Intent(getApplicationContext(),Register.class);
        startActivity(intent);
    }
}

Register
import android.content.DialogInterface;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;

import com.android.volley.AuthFailureError;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.util.HashMap;
import java.util.Map;

public class Register extends AppCompatActivity {
    Button reg_bn;
    EditText Name,Phone,Email,Password,ConPassword;
    String name,phone,email,password,conpass;
    AlertDialog.Builder builder;

    String reg_url = "http://IP_ADDRS/VolleyAndroid/register.php";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_register);
        reg_bn = (Button)findViewById(R.id.registerbtn);
        Name = (EditText)findViewById(R.id.nameedit);
        Phone = (EditText)findViewById(R.id.phoneedit);
        Email = (EditText)findViewById(R.id.emailedit);
        Password = (EditText)findViewById(R.id.passedit);
        ConPassword = (EditText)findViewById(R.id.cpassedit);
        builder = new AlertDialog.Builder(Register.this);
        reg_bn.setOnClickListener(new View.OnClickListener(){

            public void onClick(View v)
            {
                name = Name.getText().toString();
                phone = Phone.getText().toString();
                email = Email.getText().toString();
                password = Password.getText().toString();
                conpass = ConPassword.getText().toString();

                if(name.equals("") || phone.equals("") || email.equals("") || password.equals("") || conpass.equals("")){
                    builder.setTitle("Something went Wrng!!");
                    builder.setMessage("Please enter all the feilds");
                    displayAlert("input_err");
                }

                else{
                    if(!(password.equals(conpass))){
                        builder.setTitle("Something went wrong!!");
                        builder.setMessage("Password incorrect!");
                        displayAlert("input_err");
                    }
                    else{
                        StringRequest stringRequest = new StringRequest(Request.Method.POST, reg_url,
                                new Response.Listener<String>() {
                                    @Override
                                    public void onResponse(String response) {
                                        try {
                                            JSONArray jsonArray = new JSONArray(response);
                                            JSONObject jsonObject = jsonArray.getJSONObject(0);
                                            String code = jsonObject.getString("code");
                                            String message = jsonObject.getString("message");
                                            builder.setTitle("Response from server");
                                            builder.setMessage(message);
                                            displayAlert(code);
                                        } catch (JSONException e) {
                                            e.printStackTrace();
                                        }

                                    }
                                }, new Response.ErrorListener(){
                            public void onErrorResponse(VolleyError error){

                            }
                        }){
                          @Override
                            protected Map<String, String> getParams() throws AuthFailureError{
                              Map<String, String> params =new HashMap<String, String>();
                              params.put("name",name);
                              params.put("phone",phone);
                              params.put("email",email);
                              params.put("pass",password);


                              return params;
                          }
                        };

                        MySingleton.getInstance(Register.this).addToRequest(stringRequest);
                    }
                }
            }
        });
    }

    public void displayAlert(final String code){
        builder.setPositiveButton("OK", new DialogInterface.OnClickListener() {
            @Override
            public void onClick(DialogInterface dialog, int which) {
                if(code.equals("input_error"))
                {
                    Password.setText("");
                    ConPassword.setText("");
                }
                else if(code.equals("reg_success"))
                {
                 finish();
                }
                else if(code.equals("reg_failed")){
                    Name.setText("");
                    Phone.setText("");
                    Email.setText("");
                    Password.setText("");
                    ConPassword.setText("");
                }
            }
        });
        AlertDialog alertDialog = builder.create();
        alertDialog.show();
    }
}

MySingleton
import android.content.Context;

import com.android.volley.Request;
import com.android.volley.RequestQueue;
import com.android.volley.toolbox.Volley;

/**
 * Created by sshank on 5/1/17.
 */

public class MySingleton {
    private static MySingleton mInstance;
    private RequestQueue requestQueue;
    private static Context mctx;
    private MySingleton(Context context){
        mctx = context;
        requestQueue = getRequestQueue();
    }

    private RequestQueue getRequestQueue() {
        if(requestQueue == null)
        {
            requestQueue = Volley.newRequestQueue(mctx.getApplicationContext());

        }
        return requestQueue;
    }

    public static synchronized MySingleton getInstance(Context context)
    {
        if(mInstance == null)
        {
            mInstance = new MySingleton(context);
        }
        return mInstance;
    }

    public <T>void addToRequest(Request<T> request)
    {
        requestQueue.add(request);
    }
}

My layout files
activity_main
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_main"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.company.sshank.volleyimplementation.MainActivity">

    <TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Easy Travel Connect"
        android:textAlignment="center"
        android:textSize="25dp"
        android:layout_marginTop="35dp"
        />
    <RelativeLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:id="@+id/block1"
        android:layout_below="@+id/title"
        android:layout_marginTop="50dp">
    <TextView
        android:id="@+id/emailtxt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Email"></TextView>

    <EditText
        android:id="@+id/emailln"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:layout_below="@+id/emailtxt"></EditText>

    <TextView
        android:id="@+id/passtxt"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Password"
        android:layout_below="@+id/emailln"></TextView>

    <EditText
        android:id="@+id/passln"
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:layout_below="@+id/passtxt"></EditText>

        <Button
            android:id="@+id/login_btn"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/passln"
            android:layout_marginTop="25dp"
            android:text="Sign In"></Button>
        </RelativeLayout>

    <RelativeLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:id="@+id/block2"
        android:layout_below="@+id/block1">

        <TextView android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:id="@+id/registerlink"
            android:text="Not a user? Connect now!"
            android:onClick="register"
            android:gravity="center"
            android:layout_marginTop="10dp"/>

        <TextView android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:id="@+id/terms"
            android:layout_below="@+id/registerlink"
            android:text="I Agree to the terms and conditions"
            android:layout_marginTop="120dp"
            android:textStyle="bold"
            android:gravity="center" />
    </RelativeLayout>
</RelativeLayout>

activity_register
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/activity_register"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.company.sshank.volleyimplementation.Register">


    <TextView
        android:id="@+id/title"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Easy Travel Connect"
        android:textAlignment="center"
        android:textSize="25dp"
        android:layout_marginTop="25dp"
        />
    <RelativeLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:id="@+id/block1"
        android:layout_below="@+id/title"
        android:layout_marginTop="30dp">

        <TextView
            android:id="@+id/nametxt"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Name"></TextView>

        <EditText
            android:id="@+id/nameedit"
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_below="@+id/nametxt"></EditText>

        <TextView
            android:id="@+id/phonetxt"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Phone"
            android:layout_below="@+id/nameedit"></TextView>

        <EditText
            android:id="@+id/phoneedit"
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_below="@+id/phonetxt"></EditText>

        <TextView
            android:id="@+id/emailtxt"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Email"
            android:layout_below="@+id/phoneedit"></TextView>

        <EditText
            android:id="@+id/emailedit"
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_below="@+id/emailtxt"></EditText>

        <TextView
            android:id="@+id/passtxt"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Password"
            android:layout_below="@+id/emailedit"></TextView>

        <EditText
            android:id="@+id/passedit"
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_below="@+id/passtxt"></EditText>

        <TextView
            android:id="@+id/cpasstxt"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="Confirm Password"
            android:layout_below="@+id/passedit"></TextView>

        <EditText
            android:id="@+id/cpassedit"
            android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:layout_below="@+id/cpasstxt"></EditText>

        <Button
            android:id="@+id/registerbtn"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@+id/cpassedit"
            android:layout_marginTop="15dp"
            android:text="Register"></Button>
    </RelativeLayout>

    <RelativeLayout
        android:layout_height="wrap_content"
        android:layout_width="match_parent"
        android:id="@+id/block2"
        android:layout_below="@+id/block1">

           <TextView android:layout_height="wrap_content"
            android:layout_width="match_parent"
            android:id="@+id/terms"
            android:layout_below="@+id/registerlink"
            android:text="I Agree to the terms and conditions"
            android:layout_marginTop="10dp"
            android:textStyle="bold"
            android:gravity="center" />
    </RelativeLayout>


</RelativeLayout>

Php files.. here im retrieving and inserting data
login
<?php
$host = "localhost";
$user = "username";
$pass = "";
$db = "db_name";
$conn = mysqli_connect($host, $user, $pass, $db);


    $email = $_POST['email'];
$password = $_POST['password'];


$query = "select * from Login where email like '".$email."'and password like '".$password."';";
$result = mysqli_query($conn, $query);
$response = array();

if(mysqli_num_rows($result)>0)
{
    $row = mysqli_fetch_row($result);
    $name = $row[0];
    $phone = $row[1];
    $code = "login_success";
    array_push($response, array("code"=>$code,"name"=>$name,"phone"=>$phone));
    echo json_encode($response);
}else{
$code = "login_failed";
    $message = "User not found...Please try again...";
    array_push($response, array("code"=>$code,"message"=>$message));
    echo json_encode($response);
}


mysqli_close($conn);
?>

Register
<?php
$host = "localhost";
$user = "username";
$pass = "";
$db = "dbname";

$conn = mysqli_connect($host, $user, $pass, $db);

$name = $_POST['name'];
$phone = $_POST['phone'];
$email = $_POST['email'];
$password = $_POST['password'];


$query = "select * from Login where email like '".$email."';";
$result = mysqli_query($conn, $query);
$response = array();

if(mysqli_num_rows($result)>0)
{
    $code = "reg_failed";
    $message = "User exist";
    array_push($response, array("code"=>$code,"message"=>$message));
    echo json_encode($response);
}else{
    $query = "insert into Login (name,phone,email,password)
            values ('".$name."', '".$phone."', '".$email."', '".$password."')";
$result = mysqli_query($conn, $query);
$code = "reg_success";
    $message = "Thank you for rgistering with us!! Now you can login!";
    array_push($response, array("code"=>$code,"message"=>$message));
    echo json_encode($response);
}

?>