A tournament is over at 12 wins or 3 losses. Each win in a tournament will increase your final reward.
In a tournament you may only use a booster one time, after that it will be blocked for use unless you employ coins to unlock the booster.
Common boosters can be unlocked for 50 coins, Rare boosters for 100 coins and Epic boosters for 150 coins.
Three boosters are always available, namely First Aid, Freeze Time and New Hand.
Please also note that you do not lose energy when playing in a tournament.