Best viewed on Firefox or Google Chrome (although Chrome has regressed recently!) on a decent machine.
It works on other browsers but not as smoothly and some options are limited. I'd try it on the above if I were you!
Select your faces from the dropdowns top-left or hit Luckydip, then simply click-and-drag.
Play with the controls top-right for an almost infinite number of effects. The Gallery and Randomize buttons are a good start.
Do try the different Styles as well!
Happy with your creation? Hit Send/Save and copy the link to save it or send it to the world.
Using the Add Your Own Photos buttons you can drag-and-drop images from your desktop, edit them and share! NEW! You can now use your webcam as well! (not Chrome, see above...)
You can also hit enter at any time to take a snapshot.
Turning on Go Mental (type 'm') and/or Trails (type 't') produces some interesting results too.