The included 'example.php' script invokes the classes and displayes a list of dogs from a shelter on petfinder.
You'll have to configure the SHELTER ID, API KEY and API SECRET for the script to work. Just search for those words in the file.
Currently the library is tested only against shelter.getPets - there is no reason I see that other calls wouldn't work, but if the return doesn't match that of shelter.getPets parsing into pet objects won't work. Url construction and signing still should work fine.
The library requires at least PHP 5.3, tested on 5.3.13