There are multiple sources that provide information for Star Trek, and many of them are not considered canon by Paramount for the show. But they are considered canon in the room. There are tiers of canon. Anything contradicted by a higher tier, defers to the higher tier.
1: Host decisions: Any ruling we make on the canon supersedes anything else. We don’t change too much, but what we do is for the betterment of the story. (Example: THRESHOLD IS NOT CANON)
2: Shows: The Star Trek Shows are the main canon. TNG DS9 and TOS are prioritized over Voyager and Enterprise because the latter series contradict some things in the prior series.
3: Movies: There are a few things that the movies say that are contradicted by the shows, in those cases the shows take precedence (Example: Encounter at Farpoint establishes that Federation officers do have money, which contradicts both The Voyage Home and First Contact.)
4: The Decipher RPG supplements: The Decipher supplements have a lot of useful information on planets and aliens that can be found in an easy to reference place.
5: Books: There are lots of novels, and we take into account a lot of the background information especially ships and stories about things mentioned in the show but not shown, like Picard’s stint on the Stargazer, or the Tomed incident.
6: Video Games and Comics: These are the bottom of the canon. Some ideas from these can be used, but lots of the stuff in these are contradicted by higher sources.