Basically you claim a 15-sec scene and you have 30 days to upload your piece. Most folks submit live action stuff, but there are a number of animated submissions, some quite good.
Here's the youtube link to the first effort, A New Hope:
From the youtube description:
Sounds like fun. I plan to do a scene myself.In 2009, Casey Pugh asked thousands of Internet users to remake "Star Wars: A New Hope" into a fan film, 15 seconds at a time. Contributors were allowed to recreate scenes from Star Wars however they wanted. Within just a few months SWU grew into a wild success. The creativity that poured into the project was unimaginable.
Finally, the crowd-sourced project has been stitched together and put online for your streaming pleasure. The "Director's Cut" is a feature-length film that contains hand-picked scenes from the entire StarWarsUncut.com collection.