Once you reach level 5 you will be able to join a team (not sure which one is right for you? Check out the history of the teams). You will need to be at a local gym to choose a team. Simply click on the gym and it will go through a presentation after it is over and all three teams are shown you will be able to choose one of the following: Instinct, Mystic or Valor. It is completely up to you which one you want to choose. You can pick the same team as your friends to work together, or join different teams and battle against each other! Once you join a team, you’ll gain the ability to assign Pokémon you’ve caught to open gym locations or to a location where a team member has placed one of his or her Pokémon to advance the Prestige of the gym. Click on battling a gym for more information about Prestige.