This package uses an old api version of Teamleader. To use the new version with oauth2, have a look at sumocoders/teamleader-oauth2
composer require sumocoders/teamleader
$teamleader = new Teamleader('myApiGroup', 'myApiSecret');
// do one of the calls on the teamleader object, see inline docs for more info
$teamleader->getDepartments();
PHP Teamleader is a (wrapper)class to communicate with your Teamleader-instance.
The class is well documented inline. If you use a decent IDE you'll see that each method is documented with PHPDoc.