When you have added a destination URL to your account where you want to receive the Kartra API's outbound pings, you will need a script to catch and interpret the data. Make sure it's written in a programming language that can catch the HTTP raw post request.
Here is a small PHP sample on how to get the raw post:
<?php $postdata = file_get_contents("php://input"); // the data comes as an json so you will need to decode it $postdata_decoded = json_decode($postdata); // after this you can use the info passed from kartra in your own scripts. // Ex: $postdata_decoded->lead contains the lead details that triggered the action ?>