I guess I'm not stating the question clearly enough.
A person who uses a computer that came equipped with the usual software wants to know how to get started with Linux. They don't really know what Linux is and, so far, the term distro or distribution has no meaning.
Where does one go to learn the really basic concepts that lead to using Linux? And I mean really, really basic concepts. This fictional person knows there is hardware and software, but thinks all software is, uh, software. Where does one go to get the structural relationship of microcode, BIOS, kernel, task manager, file system, window manager, compiler, interpreter, etc., etc., etc. so that one can make intelligent, informed comparisons between the various implementations of the various software components of a functioning system.