You know, I built my latest computer from scratch and I still don't entirely understand how the CPU works. I do understand that it is the part that processes information, and I have a fairly rough understanding of what kind of CPU I needed to work well with the kind of computer I wanted to build, but I think I would fail any test that happened to cover CPU uses.
I didn't need to know what it did to install the CPU and the fan though. I just needed to know how to follow simple instructions. And people who buy their computer from a store probably don't even need to know that much!