The album is a feature that allows you to view all your card series. To access it, you must enter the game's Shop and select the gem icon located on the top bar of the screen.
Once there, you will need to tap on the "Get more cards" button under the Prize Board and finally, on the "Album" button at the bottom-left corner of your screen. You can also access it via Menu > View Profile > Album.
By doing so, you will be able to view each card's information (prizes, rarity and description), add them to your dashboard and share them on your social applications.
The cards come in sets of six. As soon as you get the first 5 cards of each set, you will unlock the Special Card. This will be the rarest card in the collection and the one that will provide the best rewards.