( I see on preview that My Darn Snake Legs has alreeady posted a decent answer. Oh well, here’s mine anyway.)
In the movie, we learned that the ‘gods’ worshipped by the ancient Egyptians were in fact - surprise, surprise - aliens. Amid some newly excavated ruins, the Stargate was discovered. Young genius scientist guy figures out how to use it, and is dipatched with hardened military colonel guy to explore what’s on the other side of the gate. Confrontation with phony gods and liberation of enslaved peoples (who are descendants of Egyptians transported from Earth thousands of years ago) follows.
It’s actually more interesting and complex with that, but that’s the nutshell version. The movie had a few good and several bad points. Scientific accuracy - as is so often the case - was not it’s strong suit.
In the series young genius and hard-ass Colonel are put back to work, it having been discovered that the gate can in fact transport them a lot of different places, not just the one they already went to. They are teamed up with a military scientist, who happens to be a cute blonde woman, and sent to explore. On their first adventure, they are captured by more of the false god-guys, and escape with the help of an alien servant of the false gods, named Teal’c, who hooks up with the team and helps them with their adventures.
Again, it’s more complicated then that. The series is, IMHO, better than the movie. Not in terms of budget, obviously, but the stories are pretty good and the characters are likeable.
If you’re trying to join in part way through, a couple of things you need to know:
The ‘gods’ are called the Goa’uld. They are actually sort of parasitic; they use humans as hosts for themselves, kind of like Trills from Star Trek (if that helps). That’s one of the things they captured humans for all those thousands of years ago.
Humans are everywhere. Way back in ancient days, the Goa’uld, and humans travelled all over with the gates. There are planets throughout the galaxy with societies of humans, many of which are based on aspects of ancient earth cultures (there’s been Norse societies, Mongol societies, etc.). Some of the societies are relativelt advanced, some remain tribal. Some know about the Stargates, some don’t. Most know and fear the Goa’uld.
Hope that helps.
thwartme