Trading, one of the most requested features for Pokemon Go since launch, is finally being added. By June 23, 2018, players worldwide will be able to start adding each other as Friends, which will bring several new chances for bonuses to the game, including trading.
Enter another player’s Trainer Code, and you’ll be able to invite them to your Pokemon Go Friends List. From there, when you spin at a PokeStop or Gym, you can get a Gift. That Gift doesn’t do anything for you, but you can send it to people on your Friends List, and vice-versa. The Gifts include items, a postcard that shows where it came from, and there’s also a chance to get a unique egg that will hatch into an Alolan form of a Kanto Pokemon.
The more gifts you exchange, the higher your Friendship Level goes, which leads to more rewards when people play together. This is, of course, tied into trading as well. Nearby Friends can trade, and trading also boosts Friendship Level. Trading nets bonus candy, but does cost Stardust. But, as the Friendship Level gets higher, that cost goes down. Certain Pokemon, such as ones that are Shiny, new to you, and Legendary, can only be traded once per day with someone who is a Great or Best Friend.
Source: Pokemon Go