Cards are collectible items that you can obtain in exchange for gems in the Engine Room. To access it, you'll need to go to the game's shop, select the gem icon and press "Get more cards" on the Prize Board. This will give you access to the different card machines.
Once you place a card on the board, it will give you a special prize every certain amount of time, depending on that particular card.
You can place a maximum of three cards; our recommendation is that you select those that will give you the best rewards in the shortest amount of time.
The cards you get will be included in your Album, which you can access through Menu> View profile> Album, or Shop> Gems> Album.