Out and Back
Try riding out and back. Begin at the north trailhead (across form the paddle boat rentals). Ride a couple of miles to the group camp road (a dirt road passing through the primitive campgrounds) the cabin road (a paved road to the rental cabins) or the north trailhead. Turn around and head back. It is about 3 miles, 6 miles, or 10 miles, depending on where you turn around. Only one small climb called the Chimneys near the cabin road. The rest is fairly level and flows well.
BUMP also sponsors a Beginners ride every Wednesday at 5:30 designed for new bikers and beginners who are either just getting started or getting restarted. Might be a fun ride.
Good luck and Ride On!