As a non-Pokemon Go-er, what do the different teams mean?
I don't play it either, but I have read a lot about it. At a certain level, you are required by the game to pick a team if you want to go on, you have no choice. The teams don't really mean anything by themselves, you don't get any special or different perks from being red over being blue or yellow. As far as I know, the teams are only in regard to fighting over gyms.
I'm not sure how much of normal Pokemon you're familiar with, but in the normal games, you are a new pokemon trainer tasked with some research project by the professor of that game, who teaches you the basics. After that, you're sent out into the world to catch ('em all!) and train your various pokemon through battles with other wild pokemon. There are different geographical regions, all with their own gym and gym leader, some uber pokemon trainer. Part of the games is working your way to these gyms and battling these gym leaders (NPCs in the games).
In Pokemon Go, there are landmarks and such that are designated as gyms, such as the White House. I think (not entirely sure on this point) an un-captured gym will have a/some pokemon there, waiting for someone to come along. So the player wanders over there, battles the pokemon, and takes over that gym, after which they station their own pokemon there to defend the gym from newcomers. After that point, it's a battle to maintain control over the gym.
This is where the teams come into play. If a player on team red takes a gym, then other reds can help defend it from being taken over. If it's not defended, and a mass of blues comes over to fight, well that gym will fall to the blues.
The main question I have is whether the player has to participate in all of this team business, or of they can just ignore it and continue to collect, level, and battle pokemon. I'm not really into PvP components in games.
Similarly, World of Warcraft has a pet battle system. There are NPCs you can battle for various rewards, but you can also do PvP battles; I tend to avoid these unless I really have to do them, like for an achievement. Winning 250 PvP matches has the reward of another pet, so I did those. Winning 1000 PvP matches has the reward of an in-game title "Trainer Character Name," which I don't care about, so I won't bother with that one.