As far as I know there’s no way for server-side application to be notified by Google Drive that some file has been updated or uploaded.
But it seems the WappWolf somehow gets it, via some API – how it does that? ( see introduction video http://wappwolf.com/gdriveautomator )
There is no way to currently get notifications from Google Drive. The best way is to poll the changes feed of the Documents List API to see if a user’s Drive files have changed, which files have changed, and to act upon those changes accordingly.