Whenever you find an interesting book, but are not currently in the mood or don't have enough time to spare right now, you can simply place a bookmark inside of it, and come back to read it later.
In your "Read" menu, you'll find the option "My bookmarks", through which you can take a look on your backlog of all the books you still wanted to read (or are currently reading).
Hast du ein Buch erst mal begonnen, kannst du immer zu Beginn eines neuen Kapitels dein Lesezeichen nachrücken. So weißt du stets wo du das letzte Mal aufgehört hast zu lesen. Once you sarted reading a book, you can move your bookmark to the beginning of the next chapter whenever you finish reading one. This way, you'll always find your way back to where you left off.
Unlike favorites, bookmarks are not visible to anyone from the outside, and they don't yield any fairy dust for anyone. They are merely a tool to help you keep your adventures organized.