You get a premise for a scene, then have to write no more than five pages to a deadline. If you score highly enough, you progress through the rounds until a winner is announced.
Here's some background from the California Chronicle.
This year the competition has been reinvented to take place online allowing participants to write from a computer anywhere in the world. Like its predecessor, the scenes will still be written and judged in three rounds, with each deadline tighter than the last. However, now participants do not have to be in Los Angeles at the Expo to submit their script. This new turn has drastically driven participation up from 400 entries last year to over 2000 this year.
The Screenwriting Expo made the decision to revamp the contest out of necessity, or cancel it altogether, with the loss of revenue in the last few years. In addition, entrants expressed frustration that they were unable to attend some of the Expo classes in order to participate. The new CyberSpace Open frees the Expo patrons up to participate in all of the sessions while also inviting writers world-wide to join the event. "It really is the only writing tournament of its kind in the world. Just about any of us can write a decent scene if we have a couple weeks. But can you do it with the clock ticking, and do it better than over 2,000 others? It's a ton of fun, but most of all, it's a great motivational and learning tool for all the participants, since every scene receives feedback and guidance from the Coverage, Ink team," says Jim Cirile, founder of coverageink.com and long-time Creative Screenwriting columnist.