To add a friend to your list, please ask for their PlayerID. The PlayerID is displayed at the bottom-left corner of the settings menu and looks like this: #aa-aa11-11aa.
Once you have your friend’s PlayerID, open the “RANKINGS” menu (the golden goblet on the Arena screen) and select the leftmost tab. Tap on the “+” icon at the bottom and enter the PlayerID. If the number is correct, you’ll be able to add your friend to your rankings and you’ll see their name on the list.
You are ready to compare scores and play Friendly Matches!