The goal of this tournament is to collect as many green gems as possible while completing a level.
To take part in the tournament, you should collect at least 20 green gems, win the level, open the tournament window, and claim the gift. The stones you collected are only counted if you successfully complete the level. If you fail to complete the level, the stones you collected are lost.
After you claim your gift, you are added to the list of tournament participants in one of the leagues. You can collect gems by completing levels in both town buildings and temporary events.