on 03-22-2013 01:39 PM
The Free Friday posting has a picture of the book cover with a link to the book's page. Just click on it and you'll be redirected to the book. Instead of the "Buy Now" link for a book that has a price, you'll see a "Download Now" button. Click on it. You'll be asked to confirm. Once you do, you have "bought" the free book and your Nook will automatically download it the next time you refresh.
I'm sure someone who has an HD can tell you how to get there directly (I assume there's a way), but you can always just use your web browser every Friday to point to bn.com/unbound and follow the links from there there.