I don't have much to add to Dave's description. Courses are marked with contruction cones, and usually set up early in the morning. There is time between tech inspection and the first car off to 'walk the course'. This is where you form you plan of attack. Brake here, shift there, watch out for that patch of gravel...etc. The cars are grouped by class, so you compete against like models (for the most part). Vettes vs. RX7s, Mustangs vs. Camaros, Focus vs. Kias. The Contours (in stock form) compete against other 4-door sedans in G-Stock. Fastest time around the course in your class walks away with the trophy.
It was Buckshot77 that rolled over on the Go-Kart track.
On a side note...AutoX is highly addictive. Those that compete are usually hooked for life, and spend kagoobagoogs of money on it. Caution should be taken. That said, though, it is a heckuva a great way to spend a Sat/Sun.
Give it a try, and have fun.
Sincerely,