The Park entrance is on the West side. You can't miss it. Follow the park roads west to the very end of the lake. Park where the road begins to cross the dam. You should see many cars with bike racks around here.
Discretion is the better part of valor.
Never be ashamed to push your bike through something that you think is beyond your skills. There is quite a bit of enjoyable single-track here to keep your skills honed. Don't expect Moab-like riding here but you won't be bored either. These trails are comprised almost entirely of twisty single track with lots of climbs and descents. These trails are popular so expect to see other cyclists and maybe a horse.