Driver's Ed is your chance to progress beyond autocross which requires you to exit the track after each lap. Unlike autocross, you remain on the course for the entire session. Also, cars are sent out on the course in groups, not individually. This means that in addition to finding the fastest/safest line around the course, you must also deal with traffic. Inevitably, cars will bunch up, and passing is a required and expected part of a practice session.
Driver's Ed let's you experience continuous lapping, limited passing in a highly structured fashion, and experience faster speeds than would be found in an autocross format, without having to worry about your lap times, as DE's are not timed.
DE's (as they are known) can be run in a large parking lot (like an autocross) or on a real race track. Tracks are designed or chosen to provide a fun and challenging test of your driving skills, and prepare you for higher speeds. Instructors are always available to assist new student drivers, or those wishing to improve their driving skills. DE's are the stepping stone between Autocross and Club Racing.