OpenGL/Windows programming

Can anybody assist me? I'm trying to learn openGL through C++, and I've got the basics down, but only memorized. I don't understand yet why what works actually works; I need to learn some basics of windows programming (i.e. rendering context, device context, window handle, etc. stuff like that, though I already know what those particular terms are). Basically I need to learn more about the Windows API, I think.

The books I've seen all seem to assume you already know about that kind of stuff; nobody explains it in detail. For example, a C# book gives me some stuff about some function called "Manager.CheckDeviceFormat()" as if I already know what it does and what the arguments are.