Anyone can join, and anyone can view the bookshelf and the discussions. All members should also be able to add books on the shelf. I've added quite a few so far, but anyone joining the group is encouraged to add all books that they think may be interesting to the group. Either books you've read or are reading, or books you just have heard about or think they seem interesting. You can also add books that you don't like if you want - we can then discuss on the board which books you would actually recommend and which not.
I've only started the group, so there aren't many discussion topics yet and I haven't added all the books that I could add on the bookshelves. But I will continue working with it. I hope that there will be some active members joining! Though of course you can also join just to watch if you don't want to participate in discussions or add books.