Won't go into too much detail now as there's plenty written about these rides elsewhere on the internet. Notably, see the Fat Hippy's Blue Mountains rides (link below).

The easiest ride you could probably do here would be to drive to The Oaks Picnic area (on the main firetrail) as there are no locked gates to get in your way. Should be OK in a 2WD but after climbing up from the creek crossing the sealed road ends and can get quiet corrugated (which isn't nice to cycle on either). Anyhow, for that easy ride, park up and head to the Nepean lookout and back, around 10Kms round trip of nice undulating track.

Of course, most people will be a little more hardcore and want more distance from this, so here's a brief overview of the trails:

The Oaks Firetrail

The main trail running from Woodford to Glenbrook. Get dropped off or take the train to Woodford and ride it in the downward direction only, or do it tough and cycle up then down. Tough climbs in both directions, just more of them heading up. Fantastic single track section to the left of the main firetrail shortly after the gate near the picnic area.

St Helena Track

Very technical trail that splits from main firetrail near the top (about 5Kms in?). See St Helena for more detail.

Nepean Lookout Firetrail

As mentioned above, nice and easy ride to a top view:

Why not take in the Pisgah Rock Trail on the way, it's only an extra 700m one way?

Pisgah Ridge Firetrail

Don't know - haven't been there, splits away from Nepean Lookout at a hard right in the road (and there's also a small carpark to the left there).

Red Hands Firetrail

Don't know - haven't been. But there's some cave paintings at the end of this (which can apparantly be driven the whole way). A walking trail is marked as joining back up to the creek crossing on the main Oaks Firetrail.