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.