Your friends list can be found in the War Room , at the bottom of the page.
You can fight against the Defensive Decks (see Fortress Army ) from your friends as many times you like. This is a great way to test your decks against other players before you enter a tournament.
You will get 200 Silver when you win against any of your friends, this can be repeated 20 times a day. After 20 battles you can still continue fighting but you will not receive a reward for it.
There are a few extra rewards available for fighting against your friends. See Achievements for more information.