访问PHP页面URL？

I am recently working on a php project. I created the template for my site and design the pages. However, the navigation between pages is like the following:

http://localhost:81/x/y/index.php and when I want to navigate to another page the URL will be like: http://localhost:81/x/y/second.php

how can I make the following URL takes me to the second.php page?

http://localhost:81/x/y/index.php?page=second

Thanks.

Unless I am misunderstanding something, put this at the top of the index.php page:

<?php
if($_GET['page'] == "second")
{
    $newURL = 'http://localhost:81/x/y/second.php';
    header('Location: ' . $newURL);
}
?>

See How to make a redirect in PHP?

I would add a bit more to it to make it secure but the simple answer would be...

if(isset($_GET['page'])
{
    require '/path/to/folder/' . $_GET['page'] . '.php';
}

If it is a redirection that you want, you could also do.

if(isset($_GET['page'])
{
    header('Location: ' . $_GET['page'] . '.php');
}

Try this Rule:

Options +FollowSymLinks
RewriteEngine On
RewriteRule ^x/y/index.php?page=(.*)$ http://localhost:81/x/y/$1.php [R=301,L]