Each Season you can earn up to 30 rewards by collecting Season Tokens.

You can view these rewards by selecting the "Season" section that appears on the main menu screen next to your Free Chest.

 

Once you have accessed the Season section you will be able to see the rewards tiers and how many Season Tokens you need to collect to earn your next reward.

 

Season Tokens can be found in Chests and can be earned by completing Challenges.