Skillz is 100% free to join, and each Skillz-enabled game has numerous free-to-enter tournaments. Skillz also offers tournaments featuring real-money prizes which cost as little as $0.60 to enter. In order to play for money, you'll need to make a deposit on the system by navigating to the Store page:
Once you've made your deposit, you'll then navigate to the Play page, where you can choose your entry fee!
