Fatal error: Uncaught Error: Call to undefined function mysqli_connect() in /data/dbconnect.php:12
Stack trace:
0 /data/index.php(4): require_once()
1 {main}
  thrown in /data/dbconnect.php on line 12

<?php

    // this will avoid mysql_connect() deprecation error.
    error_reporting( ~E_DEPRECATED & ~E_NOTICE );
    // but I strongly suggest you to use PDO or MySQLi.

    $dbHost = 'localhost';
    $dbUsername = 'root';
    $dbPassword = '';
    $dbName = 'phpmyadmin';

    $conn = mysqli_connect($dbHost, $dbUsername, $dbPassword, $dbName);
    $dbcon = mysqli_select_db($dbName);

    if ( !$conn ) {
        die("Connection failed : " . mysqli_error());
    }

    if ( !$dbcon ) {
        die("Database Connection failed : " . mysqli_error());
    }

    $db = new mysqli($dbHost, $dbUsername, $dbPassword, $dbName);

    if ($db->connect_error) {
        die("Connection failed: " . $db->connect_error);
    }
?>

<?php
    ob_start();
    session_start(); // Starts the session
    require_once 'dbconnect.php';// Import the file "dbconnect.php" which is the connection of project with the database

    if ( isset($_SESSION['user'])!="" ) { // It will never let you open index(login) page if you are logged in
        header("Location: home.php"); // Automatic send to home.php and blocking index page.
        exit;
    }

    $error = false;

    if( isset($_POST['btn-login']) ) {

        // Prevent sql injections (attacks) / clear user invalid inputs
        $email = trim($_POST['email']);
        $email = strip_tags($email);
        $email = htmlspecialchars($email);

        $pass = trim($_POST['pass']);
        $pass = strip_tags($pass);
        $pass = htmlspecialchars($pass);
        // Prevent sql injections (attacks) / clear user invalid inputs

        // If there's no error this code allows the user to log in:
        if (!$error) {

            $password = hash('sha256', $pass); // Password hashing using SHA256 it is encripting of the password that the user is entering so that third people cant read it, to check it do SELECT * FROM users;
            $res=mysql_query("SELECT userId, userName, userPass FROM users WHERE userEmail='$email'"); // Takes the data from the database where the userEmail is equal to the $email that has been inserted
            $row=mysql_fetch_array($res);   // $row = mysql_fetch_array($res)it is returning the row
            $count = mysql_num_rows($res); // If the mail and password correct, it will return only one row

            if( $count == 1 && $row['userPass'] == $password ) { // it is taking the userPass and user Id for the session, if the data inserted during login is correct (rest of description line 50) -
                $_SESSION['user'] = $row['userId'];
                header("Location: home.php"); // - header("Location: home.php"); moves the user to the home.php just if the users data is correct
            } else {
                $errMSG = "Incorrect Credentials, Try again..."; // returning error if anything goes wrong.
            }

        }

    }
?>