Tribal Rewards are earned by contributing to your Tribe on Tribal Island. 

When Tribal Island resets each week, all active Tribe Members will receive Rewards based on the Tribe's Level and their individual Monster Level. Also, the Levels of all Monsters on Tribal Island and the Tribe Level will be reset back to 0 so you can earn more rewards the following week!

You can see the Rewards your Tribe has earned for the current week, and how much time you have until the next reset by clicking on the Tribal Rewards Button.