You have a profile, and you write reviews and give ratings to books you've read. But that's just the beginning. You can also connect with your friends, show them your bookshelf, see theirs, do trivia, write poetry or your own book, and even meet the authors of the books you've read. Within the classroom group, you can have ongoing discussions, give short quizzes, do polls, just let students discuss books with one another, and get recommendations for books based on your history of reading and ratings.
It's a valuable tool to use for your class. Students can use it to keep a log of what they've read, to express themselves to their classmates, and most importantly, to get excited about literature. I recommend this site, it is a little work to set up, but well worth the effort.