In the 'Round Setup' screen tap on 'Add Player'.
You may opt selecting from Buddies, Facebook, Contacts or by tapping the '+ Icon' in top-right to add a new buddy.
Input all details and tap 'Add' when done.
Once a player is created, you will see them in the Players section, so you can check that is everything set correctly before you start your round.
Note: Email is required in order to automatically send the round scorecards to your buddy.