//----- CONNECT TO DATABASE -----
	$dbname = "database_name";
	$dbusername = "user_name";
	$dbpassword = "password";
	mysql_connect("localhost", $dbusername, $dbpassword, $dbname) or die("cannot connect");
	mysql_select_db($dbname) or die(mysql_error());		//Select the database so it doesn't need to be specified in mysql functions

Example Config File

config.php

<?php
  //Main Database:
  $main_db_host = 'localhost';			//Typically "localhost" or IP address if on another server
  $main_db_name = 'MY_DATABASE_NAME';
  $main_db_username = 'USER_NAME';
  $main_db_password = 'PASSWORD';
?>

PHP Files Using The Database

include_once('config.php');

//----- CONNECT TO DATABASE -----
mysql_connect($main_db_host, $main_db_username, $main_db_password, $main_db_name) or die("cannot connect");
mysql_select_db($main_db_name) or die(mysql_error());		//Select the database so it doesn't need to be specified in mysql functions