There was the movie. Roland Emmerich planned to make a couple of sequels turning it into a trilogy, but that never happened. Bill McCay wrote a short series of novels based on the premise of those sequels through the late 90's.

The TV series Stargate SG-1 treats the movie as like 96.7% canon. There are some very minor things directly retconned, for example in the movie the nameless planet they go to is said to be in the "Kaliem galaxy" where in the show the same place is named Abydos and is located in the Milky Way galaxy, but beyond a few details like that it is treated as established fact.

TV show picks up from where the movie left off, then takes a 27° right turn and heads off in its own direction compared to where the books went. It kind of feels like the writers were given nothing but the theatrical cut of the movie to study with no other context or creators' notes or anything, and then told to make a TV show out of it. And then they did a very good job with this assignment.

You know how some shows have a first season problem? Like, Babylon 5's first season is a little rough and it really gets good in Season 2, or how you should introduce someone to Star Trek TNG at Season 3? SG-1 has some early installment weirdness in the first six episodes or so but they're watchable, and then by mid-season 1 it finds its groove.