How can I solve the issue below?

See more:

HTML

PHP

First chek this simple code: ...............................................................................................................................................................

<?php
$mysql_host = 'localhost';
$mysql_user = 'root';
$mysql_pass = '';

@mysql_connect($mysql_host, $mysql_user, $mysql_pass) or die('Couldn not connect.'); echo 'Connected!';
?>
.................................................................................................................................................................

When I try to run the code above using Xampp server, the following error appears: ..............................
Fatal error: Uncaught Error: Call to undefined function mysql_connect() in C:\xampp\htdocs\Series\database\index.php:7 Stack trace: #0 {main} thrown in C:\xampp\htdocs\Series\database\index.php on line 7
...............................

I really need to sort thus out.

What I have tried:

I have no idea how to sort this