Great question! The prep work introduces you to the fundamentals of Ruby. It consists of approximately 100 hours of work in total, and is a good minimum preparation set for the course.
The students who have prepared the most for the course also get the most out of it. They are able to breeze past easier concepts and study more complex concepts in depth. Accordingly, we do strongly recommend preparation beyond the required prep work. We have found that the best preparation is completing problems/projects (vs reading). You can find many interesting problems at: