Join a Team!
At a certain point in the game, you'll be asked to join a team. Pick the same team as your friends to work together, or join different teams and play as rivals! 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.
Once you join a team, you can assign Pokémon you've caught to an open Gym or to a Gym where a team member has placed one of his or her Pokémon. Like PokéStops, Gyms can be found at real locations in the world. Each player can place only one Pokémon at a particular Gym, so you're encouraged to work with others on the team to build up a strong defense.
Every Gym has a Prestige amount that determines how difficult it will be to take it over. Training Pokémon at your Gym will increase its Prestige, while losing battles to other teams' Pokémon will lower it.
If you visit a Gym that's already controlled by your team, you can train there by battling against your own team's Pokémon! If you manage to defeat all of them, your Gym's Prestige will go up, making it more difficult to defeat by another team.
Use your own Pokémon to challenge Gyms claimed by other teams. With the Pokémon you've caught, engage in battle against the defending Pokémon at the Gym to claim control!
Battles are challenging and fun! Use your Pokémon's two moves to battle the defending Pokémon. You can also dodge the defending Pokémon's attacks by swiping left and right.
If the Gym's Prestige is reduced to zero, the defending team loses control of the Gym, and you or another player can then take control of it by assigning a Pokémon to protect it.
Assign a Pokémon to a Gym already controlled by someone on your team to add to that Gym's defense. Every Pokémon added by a team member will make it that much harder for an opposing Trainer to defeat your Gym. Remember—you can leave only one Pokémon per Gym, so get help from friends!