Custom courier company toolbar – where to place it?

Could you help me with this :
<?php
session_start();
$user_id = get_current_user_id(); ?;
if(!empty($user_id)) {
echo file_get_contents(“https://www.econt.com/voffice/728×90/?mediator=http%3A%2F%2Fbigsalebg.com”&client=&#8221;.$user_id);
} else {
//…
}

It is a code that the courier company gave me (I even don’t know if it is complete) and told me to integrate it to my site so that the users can use it to prepare the delivery themselvels.

The thing is I simply don’t know where to place it. I have tried to add it to functions file in my Child theme but my site stopped working 🙂

Help please!