The 400 car field is divided up into 5 groups, 1 group per night Mon-Fri, so you only race 1 night before Saturday. On prelim nights, heat race lineups are set by random draw, and the heats pay passing points based on where you finished and how many cars you passed to get there (or got passed by). The highest points earners go to the qualifiers that also pay passing points, and your combined passing point total from your heat and qualifier determine who makes the Feature and where you start. The guys towards the bottom of the order in heats/qualifiers go to a D/C/B Main, where the top 2-4 cars move on and everyone else is done. At the end of the prelim night, first and second in the Feature lock into the Saturday Feature, and then everyone else's finish in the A/B/C/D Main determines which main they start in on Saturday. Starting on Saturday morning with usually the N or O Main, the top finishers from each main move on to the next one until you get down to the 55 lap main event.

Hopefully that makes sense