The main themes presented in the second episode of SG-1 are Teal'c's acceptance by the SGC and his appointment to SG-1, and the knowledge gained about the goa'uld themselves. These are presented as two side-by-side stories which resolve together at the climax of the episode. In one story Teal'c is being held prisoner by the USAF for questioning and study, with O'Neill being the only one who trusts him completely. During interrogation he reveals the knowledge that the goa'uld control hundreds if not thousands of worlds in the galaxy by posing as gods to humans and jaffa. It is also revealed that Earth is the legendary Tau'ri, the homeworld of the human form from where the original people were taken by the goa'uld and used as hosts, modified into the jaffa, and kept as slaves.
The second story follows Major Kawalsky as the characters realise he has been infected with a goa'uld symbiote. The symbiote at various points takes control of Kawalsky, killing one man and hurting several other people. The doctors on base attempt to cut it out of him but ultimately fail, and the episode culminates in a battle between Kawalsky, who is trying to return to Chulak through the stargate and destroy the SGC in his wake, and Teal'c, who affirms to General Hammond that he has truly forsaken his former masters by killing the goa'uld (and , sadly, Major Kawalsky in the process).
It's a shame to see Maj. Kawalsky killed off so early in the show as he was a strong character, and a carryover from the film. He does return for one or two cameos in future episodes but as far as the main storyline is concerned, he's dead for good. His death, though, brings around something good - Teal'c as a member of SG-1. The final shot of the episode confirms this as we see the team march, in matching fatigues, up the ramp and through the stargate on the first of their many missions.
A smaller story which is easy to miss is that of General Hammond becoming less of a hardass than in Children of the Gods - he still retains the quality in his first scene of the episode, but throughout the course of the show he sees how badly other members of the US Government are willing to treat Teal'c who is still (almost) a human being and decides to be more trusting of O'Neill's judgement of the man, as well as letting his actions speak for themselves. It's important that the General is seen to be 'one of the good guys', as he is after all Jack's boss and will be giving many of the orders throughout the show.
Tomorrow's episode, Emancipation, is a rather weak one, but is the first planet-of-the-week style episode, a format that I really enjoyed through the early seasons of SG-1.
P. S. Did you notice the scenes in this episode where Teal'c's forehead emblem was upside-down? In these early days, it was applied in three parts rather than one, and the makeup crew were still getting to grips with spending an hour applying it to him every morning.