Different tournaments end when you have completed the number of wins required or after losing a certain number of games in that tournament.
Small tournament - Ends in 7 wins or 2 losses. Costs 15 gems/1 purple ticket to enter
Big tournament - Ends in 5 wins or 1 loss. Costs 30 gems/2 purple tickets to enter
Gold Tournament - Ends in 7 wins or 2 losses. Costs 800 coins/1 orange ticket to enter.
Keep in mind that boosters can only be used once during the same tournament. If a booster is used in a tournament, you will need to unlock it using your coins to use them on your next matches for that particular tournament. You can refer to the list below on the cost of unlocking boosters per rarity.
Regular boosters - 50 coins
Rare boosters - 100 coins
Epic boosters - 150 coins
Legendary boosters - 200 coins
There are 3 boosters that you can use in the entire tournament at no cost. These boosters are Amplify, Freeze Time, and Go Fish. Tournaments also do not consume energy.