Technically, I think they split things into "canon" (movies and novelizations of the movies), "official" (approved EU stuff), and "unofficial" (some of the older comics, ewok movies, holiday special). The "official" label basically means other people making official stuff has to take it into account, but Lucas doesn't.Ankh-Morpork Guard said:Actually, anything not invalidated by Lucas' works are canon.Lucas Licensing deals with all of that kind of thing.
As for what they can do... the things we see in the movies are basically telekinesis, personal augmentation, sensing things, mind-control, and force lightning. Of these, force lightning seems to be Sith-only, as are some uses of the other powers (e.g. TK choke).