<?php
    //You will want to create a database connection class
    //in the future instead of using variables
    $dbhost = ''; //Database host
    $dbuser = ''; //Database username
    $dbpass = ''; //Database password
    $dbname = ''; //Database name

    //Connect to MySQL
    $con = mysqli_connect($dbhost,$dbuser,$dbpass,$dbname);
    if (mysqli_connect_errno())
    {
        echo 'Cannot connect to the database:' mysqli_connect_error();
    }

    //Check the user
    if(isset($_POST['login']))
    {
        $user = mysqli_real_escape_string($con,$_POST['user']);
        $pass = mysqli_real_escape_string($con,$_POST['pass']);
        $run_user = mysqli_query($con, "SELECT * FROM `UserName` WHERE userName = '$user' AND pass = '$pass'");
        $check_user = mysqli_num_rows($run_user);
        if($check_user > 0)
        {
            $cookie_name = "user";
            setcookie($cookie_name, $user, time() + (86400), "/"); //Set cookie for 1 day
            $_SESSION['User'] = $user;
            echo "Logging in as ".$user."...";
            header("Location: /adminpanel.php"); //Use header instead of a javascript
            exit;
        }
        else
        {
            echo "Error during login, check user/pass";
        }
    }
?>