When you learned to drive a car you learned also more then just how to handle the steering wheel.
Every chapter starts easy and gets more difficult to the end.
If you feel you lost track or got bored, skip that part and read it later if you feel like it, or use it as a reference, when you need it. First a little convension that we want to use. The normal perspective of a computer in a layered model is the hardware at the bottom and the software running on top of the hardware. We will toss that around. We put the hardware at the top.