Don't feel bad if you have questions man, that's what we're here for.
The HPR and LPR are both regulators. The LPR is the low pressure regulator on the front of the gun, and the HPR is the high pressure regulator that serves as the front grip. For the most part, the HPR is for setting velocity, but the LPR also plays a role, and if it's set too low, the gun won't cycle. Usually you can set either reg to a certain pressure, then adjust the other to get your desired velocity. The ram is what the bolt is connected to via the bolt pin. It is supplied air from the solenoid, moves forward, hits the valve and opens it for a split second, which sends air up through the bolt and fires the ball, and then the solenoid clicks back off and the ram retracts. All of that happens in a tiny fraction of a second.
I hope that gave you a bit of an idea of what the parts do. Do a bit of searching and you'll find more, and you may also want to check out the PBnation ICD forums and search there as well.
few questions... im pretty new =[
