https://www.polygon.com/2018/6/18/17474184/pokemon-go-friends-list-how-to-trade

An update will go live for Pokémon Go users this week, Niantic announced. The update is one of the game’s biggest ever, adding features that many current and former players have anticipated since Pokémon Go’s 2016 launch: trading and a friends list.

Friendship in Pokémon Go comes with special bonuses, according to Niantic. The social feature will encourage players to exchange six-letter, personalized Trainer Codes (think Nintendo’s Friend Code system) in order to add each other to their list of friends. Once a friend request has been accepted, trainers then can check out their friends’ stats in the main profile screen, including what their most recent in-game activity was.