Bowen Kerins runs it. It's a standard unlimited qualifying entry format. Last year there was a modern and classics division with (I think) five games per bank.
You want to have a good enough score to qualify by the end of the qualifying period, which is around noon on Sunday. You can purchase as many entries as you like to do so. CAX tends to be very competitive so it can take a lot of work to qualify.
For novice players, which for CAX is defined as "never won a cash prize in a pinball tournament", you play both banks and there is a novice-only finals. If you place high enough, however, you play in the Open finals. I won novice in 2010. I got a t shirt, $150 and a big trophy. I spent about $90 in qualifying.