You can find here the documentation for the AtOnline API.
On the right of this page are a list of namespaces, containing themselves either more namespaces or methods and some of which can be accessed. The API is fully rest compliant, which means objects can be retrieved (GET), updated (PATCH), created (POST), or removed (DELETE), and some have methods.
Methods are a AtOnline specific extension to rest, and can be differentiated from objects by the presence of a colon character (:) followed by the method name. Preceding this can be a full rest path, with object names and keys, and while some methods are static, some other will need an object key to be usable.