I made a very simple Facebook application in PHP that retrives information about the current logged user (it looks in cookies). I am interested in retrieving information from another Facebook application: deezer, deezer facebook application. Do you have any idea of how can I access this information (from deezer, e.g. the favourite music of the current user)? From your experience, what's the approach of learning how to develop Facebook applications?
You would probably have to contact Deezer regarding services into their database. If a user has installed your Facebook application, then it would be my assumption that you have been given some sort of unique id that identifies the user. If Deezer allows it, you could give them that unique id and they could return the users music profile. If you look at thei site, Deezer does provide an API.