Like I said, it's SUPER easy. First make PDF (or Word doc) comprised of all the pages you want to include, then upload them (for FREE) to the website, and wah-la you're published! Even better, you're saving paper! I used InDesign for the layout of the pages (but you could use Photoshop, Illustrator, even Word or Powerpoint/Keynote), some product descriptions from my website for copy, and some amazing images from my photo shoot with Belle Photography for the visuals.
I plan to use my look book as a handy-dandy marketing catalog for my press kit and website. But there are numerous other uses for such an awesome tool. You could start your own magazine, make a family scrapbook for Mother's Day, start an online garage sale, create a virtual children's book (you can even add sound!), the list goes on and on.
Another great feature of Issuu is that it allows you to subscribe to various online magazines/books/etc and create a virtual bookshelf (see below). That way you can have a record of all your favorites and get notified each time a new issue is released. Go check it out for yourself!