This can be done in either direction, and doing it as an out-and-back is very "do-able" for the novice cyclist.
Starting from the Folsom Point end (fee required if you drive in), a short descent puts you on the Mormon Island Auxillary Dam (incorrectly known as "Dike 8"). Cross the dam and begin the rolling, meandering singletrack and some doubletrack for 3 miles to Browns Ravine Marina.
You can also start on the Browns Ravine Marina side.
Remember: This is a popular multi-use trail! Seeing walkers, runners, equestrians, dogs and other mountain bikers is very common. Don't go too fast, especially around blind turns. Ring your bike bell or let out a whistle or hoot when approaching blind turns. If you must listen to music, just use one ear bud! Please yield to all other trail users... surprise them with your courtesy :)
For the adventurous, there are several "social" trails heading into the hills above the official Browns Ravine trail, which allow you to add some climbing, descending and miles to your ride.
The trail East of the Marina continues 15 miles or so to Salmon Falls, but is not bike legal (yet).
If it gets too hot, pull over and jump into the lake!