Before I start, this is based on parking on the Gordon College campus. There is public parking at the trailhead, just go to the main entrance and ask the guard where to go.
This place is one of my staples. It's my go-to place when I'm on the North Shore. I always felt like it was a little bit of a secret when it comes to MTBing. For the first 1/3 mile or so, you'll find a lot of people walking to the beach on the pond in the woods, but once past that, it's open trails everywhere. You need to go a couple miles back to get to Chebacco, but it's great trails the whole way. Once you go down the fire road, you'll see some singe track up a short but steep hill to your right. There's a few short trails up there that are not too hard, I usually warm up on those. Then I head further down the fire road. You'll go around a sharp uphill left hand turb. A few hundred feet after that, there some single track trails on your left, watch carefully, they're easy to miss. Once you go in there, just keep heading back into the woods, the trails go on for miles and miles. There's a bunch to choose from back there. Everytime I go, I find more. There's also several ponds and lakes back there which are nice to stop and take a break at. There's a fair amount of bugs in this area, so bring some bug spray!
Overall, the trails are mostly intermediate. There's a little bit of easy stuff, not much advanced. I am an intermediate rider and I can handle anything there. I took a beginner with me a few times and he can handle most of the stuff but with some trouble in certain areas. There were a handful of times he had to get off his bike and walk. But don't hesitate to take a beginner here as long as they understand there's a few obstacles they may not want to attempt (logs, rocks, a couple steep hills, etc).