The only way to get to know this program is to just dive right in and start editing, using the many menu functions on the left sidebar of the site. You'd be amazed at all the fun ways you can transform images and create flyers, holiday or business event cards as well.
I have found this program to have a much faster learning curve than PhotoShop or Gimp, both of which are powerful photo editing programs. And for many reasons, PicMonkey is much more fun to use and share images with friends.
Be sure to check out the tutorials on PicMonkey.com and the many PicMonkey video tutorials on YouTube as well, such as this one which shows you how to use overlays to create the illusion of a boy flying.