If you want to override modules you have to create an extension. If you see url address chat/startchat there is 99% chance that module file is located in
if you want to override this module you have in your extension have this structure
module.php file content should the following
<?php$Module = array( "name" => "Start chat overide");$ViewList = array();$ViewList['startchat'] = array('script' => 'startchat.php','params' => array());?>
startchat.php file content can be just copied from modules/lhchat/startchat.php file. I suggest just look at customstatus extension as example. There is overriden user/login file.