To invite your friend, please follow the steps below:
1. while in the lobby, press Square to bring up the friend list
2. Once you bring up the friend list, scroll between the players in your friend list and press triangle to invite them to your Team.
3. In case you want to invite a friend, not in your friend list or is on Xbox, press the Share button that would bring up the Nickname search menu. Enter the player's nickname and then invite them to your team.