This stuff comes mainly from books or comics but also games and of course the movies(but in the 6 movies there is little information because of the main story). On every page there is the headline "appearance" where you can find them. Us crazy freaks write this because we like to know the whole story and the background of all things like the discovery of the force. And on these pages there are people of all countries like me. I am a German.
Actually, the "Extended Universe" (EU) as anything outside the movies is known, is believed to have started with the novel "Splinter of the Mind's Eye", the first EU novel. Now the EU spans games, comics, tv series, and several hundred novels, not to mention action figures, lego kits, and replicas.