How to connect to database config.php

How is that we create a php file, to connect to the database
First we need to check, the application is installed or not xampp and service for apache and mysqlnya already way or not?
if it had stayed we make koneksi.php file / config.php


<?php

$host = 'localhost'; 
$user = 'root'; 
$pass = '';


$dbname = 'dbname';
$connect = mysql_connect($host, $user, $pass) or die(mysql_error());
$dbselect = mysql_select_db($dbname);

?>