A Rallycross is basically a timed single car race through a course set up in a dirt/grass field. There are usually at least 4 separate runs for each car entered and the lowest accumulated time for all runs wins.

More info here: http://www.texasscca.org/rallyx.html

No special equipment needed except a closed top vehicle (no rag tops) and an approved helmet. There will be loaner helmets provided at the event. Each car will be inspected prior to race for working seatbelts and other safety items.