May I ask, what are the teams, and how do you join? I don't have the app yet, and I'm quite curious to know o3o
There are three teams to choose from. Team Instinct ( Yellow - Zapdos ) Team Mystic ( Blue - Articuno ) and Team Valor ( Red - Moltres )
You can join a team once you hit level 5, and find a gym. Simply tap on a gym and it will ask you which team you want to join.
The teams are for gyms and do nothing else. For example, if you're apart of Team Instinct, you can only battle at Blue or Red gyms and try to claim it for your team, but you can train at a Yellow gym.