PHP and Forms

<!DOCTYPE html>
<html>
<head>
    <title>
        <!-- bootstrap css link -->
    </title>
</head>
<body>
    <?php
        if(isset($_POST['Verify'])) //to check if the name = "submit" button was pressed
        {
            if(!empty($_POST['username']) && !empty($_POST['password']))
            {
                if($_POST['username'] == "sakib" && $_POST['password'] == "1234")
                {
                    echo "Logged in";
                    header("location: http://fb.com");
                }
                else echo "Onner account e dhukte chas ken?";

            }


        }
    ?>
    <form method="POST" action="">
        <input type="text" name="username"><br>
        <input type="password" name="password"><br>
        <!-- type can be the type of input such as button(type is submit), dropdown etc -->
        <!--name is the name of the attribute that will be used in php-->
        <!-- value is the name that will be displayed on the button or input -->
        <input type="submit" name="Verify" value="Verify">

    </form>


</body>
</html>