In a file called dbconnection.php or anyother fiting name:

<?php
    //Set strings for host, user, password and database name for access to
    //the database.
    $dbHost='localhost'; //The host name - for the time being localhost will do the job.
    $dbUser ='root'; //The name of user accessing the database - root normally has no restrictions.
    $dbPassword='password'; //Use '' if no password is set. Must be the matching user password.
    $dbName='database_name'; //Can not be NULL - you must enter a valid database name.

    //Connect to the database server.
    $dbCon = @mysql_connect($dbHost, $dbUser, $dbPassword);
        if(!$dbCon){
            echo("<p>Cannot conect to the database server.</p>");
            exit();
        }

    //Connect to the database.
    mysql_select_db($dbName, $dbCon);
    if(!@mysql_select_db($dbName)){
        echo("Cannot locate ".$dbName." database.</p>");
        exit();
    }
?>