Newegg has a series of videos explaining some basic details about different components, but it's more about walking through a build than explaining what the components do and how they interact.
the videos are in the middle of the page.
More time-consuming method:
Get your hands on a comptia a+ study manual and read it. It will take longer, but you'll have a more thorough (and especially windows-based) understanding of how the pc works and some networking technology as well. It's basic, but a good place to start.
I expect I'll some hatred here about the mention of a+...
If you're trying to get a quick view into the idea of a pc build, I recommend the newegg videos.
the operating system (win7, win8, a linux distro...) wouldn't determine the overall build, but a basic gaming pc running windows (and/or Ubuntu Linux now that Steam is available on it. I have a friend who plays nothing but Borderlands 2 from Steam on a gaming laptop running ubuntu) would definitely be a good first project because you'll have to do some research and even a basic gaming rig will more than likely contain all of the same components (albeit at a lower price and/or performance) as you'd see in many other types of builds later on as you get more advanced.