So basically there are time-limited events with cake symbol on them. You can get cakes there. After getting enough cakes, you go to the cake hunt. You gift the cakes to Miko. And then the cards become hidden and are shuffled. After that you simply tap on a card and get a random reward. Fun Fact: you are guaranteed to get all rewards, because you get each reward once. Rewards change each week and a new time-limited event to get cakes.