Do mountains and piles of books line your shelves? When is the last time you actually read any of those books? Shouldn't someone who hasn't read them get a chance to? Don't the rest of your belongings deserve a chance to not be in piles on your floor? Exactly.
The comm itself is simple: After reading THE VERY HELPFUL FAQ POST you post with a review, short or long as you want, about a book you've read. Register it with BookCrossing. If someone within whatever timeframe you specify (no more than two days) wants that book, they will contact you in order to get it! If nobody claims it, you leave it somewhere in the wild and move on to that next book on your list.
But what if I want to review the book and keep it? Or, do I have to post reviews at all? This is...well, I can't say that you can't keep your own books. That would just be silly. But the point of the comm itself is to get rid of the books you don't want in your room any more. And yes, if you want to be a part of the comm just for some free books, this is highly encouraged! We hope you find something you like.