I don't have a cute story behind this REALLY fun new toy; it's just cool.
When you think you're done, you can look at the finished poster, then go back and edit it to tweak it until it looks just the way you want it to. When you really are done, you can save your image to your hard drive or purchase a large, professionally printed copy for yourself.
I've been playing with this for the past couple of days and I'm having WAY too much fun with it.
Here are some other movie posters I've made over the past day or two: