Cards are collectible items that you can get in the Machine Room in exchange for gems. To enter the room, tap on 'Get more cards' on the board of the main screen of the game.
Each card will give a special prize in a specific time lapse, and both the prize and the waiting time will depend on each particular card.
You will be able to place a maximum of three cards on the board and we recommend you pick the cards that will give you the best rewards in the shortest possible time.
Every card you get will be included in your card collection, which you will be able to see by going to Menu>See profile>Card Collection