Windows Registry doesn't really have anything to do with anything, it's just a (really dumb and vulnerable) way Windows keeps up with programs.
If you want to learn how computers work, I'd start by reading lots of Wikipedia articles. You don't need to know how to program to know how computers work. I'd start with pages like
Random-Access Memory, the
Von Neumann architecture (the architecture pretty much all moder computers follow (not exactly, I know it's modified, but you know)), how a
CPU works, and also I'd even advise to read up on computer history, since old computers don't hide anything from you, so they go into a lot of detail about how they work. Models like the
UNIVAC,
PDP-11,
Altair 8800, and any other old machines you can find. You'll pick up on what they're trying to say in due time. Like someone else recommended, I'd also recommend installing GNU/Linux. From that you'll learn all the packages that are installed, like your init system and display server, and thus learn what those things are.
If you want to program, I'd start with training yourself on how to program. You can't write anything past "hello world" because I'm assuming your mind isn't trained to think like a programmer. I'd start really basic, like using Scratch or RPG Maker, some drag-and-drop logic system that trains you how to think in simple steps to make an automation. After you can get some sprites dancing around the screen, then I'd say you can learn a real language. Maybe JavaScript or Python, since they result in the most immedate output. Or if you like Minecraft, install the ComputerCraft mod and give Lua a whirl. And lastly, I recommend lurking communities that are into programming, like here, or maybe 4chan's /g/ or reddit (both places are awful but if you're a total beginner why not)
But I think you're certianly far away from writing an OS. This doesn't mean it'll take you a long time to know how to make an OS, but it will take a lot of learning before you can try it. When you can fluently read C and C++ (or any language, since knowing how to program means you can pick up any language with not too much trouble), and thus can read the source code of other OSes, then I think you're sufficently capable of beginning. Best of luck to you!