Every day that you complete all your health tasks, you will earn a Heart. A heart will allow you to turn on a reward brand to add it to your reward pool (this is the pool of gift cards you could win when you play a game in the app).
🔑 Note: You can only add a brand to your reward pool if it is available to your level. Levels are like having access to new doors and Hearts are the keys to unlock them.
By going to Rewards then My Hearts, you can customise your reward pool so that you only win rewards from your favourite places.
When you turn on a reward brand with your Hearts, you are not winning it, so you can't activate it (yet!). What this does is it makes it possible to win a reward for that brand every time you play a game in the app. If you leave a reward turned OFF, you will never be able to win it.
To understand how this works in detail, see What rewards can you win?
Rewards you turn on can be won multiple times, and will remain ON until you turn them off again. Learn more about winning rewards here.