When you click on the 'Collections' button at the bottom of your lobby, just to the right of the 'Piggy Bank' button, you’ll find six 'Locations' there with different themes. You need to collect 10 unique items for each locations to be filled. Every card has its own star rating, the higher the star number, the rare the card is.
After completing each book, you’ll get a completion bonus, and when you complete all the books, you get a Grand Prize!
Tap on 'Collections'