Teams
 

When you get to an airsoft sight do they split you off into teams or do you come with your own team?

That's entirely dependent on the site and game host in question. If you've arranged a team ahead of time usually there wouldn't be any problem with you going with that, especially if it's just skirmishes. If it's more milsim or some sort of scenario then the game host might want to split you up according a bunch of possible criteria.