A newbie to trails can expect to have a lot of fun. I believe most of the course will be very similar to the River Rock Scramble 10K but with a few surpirses.
The biggest difference will be that you will have to pay attention to the footing. On roads you can veg out and not really worry about placing your foot on a secure spot. Trails have rocks and roots and narrow paths. The secret is to keep your eye on the trail. When passing tell the person in front "on your left", or "on your right". The person being passed should pull off and let you go by. Do not litter, what you carry with you, GUs, Cliff bars etc, you should carry the wrappers/trash back out with you. ie trail edicate.
I've found trail running has made me a strong road runner.