It's a site where you can create your ideal cast for a book. If you were to turn it into a movie and were in charge of who was playing who. Even if it's already been turned into a movie, you can make changes to the cast or give it a more updated one. If they don't have a book you've read or an actor/actress you're looking for its pretty easy to get it added, you can just write them a message and typically the book or person will show up fairly quickly.
Well I hope you all enjoy it. I know I have.
Have a good day!