Well,

"Windows" belongs to Microsoft.............there is a hell of a difference between 2.03 and XP!

MacOS belongs to Apple.....................OSX is one hell of a lot different from the early versions?

On this site you will see the expression "*nix" not Unix or Linux...............there are many flavours of these (unix based) OSes as well, both from different suppliers and over time. For example Sun=Solaris, IBM = AIX and these are not even open source?

Either you will get very general tutorials on operating systems or quite specific ones referring to a specific version..............it is up to you to chose.

If you have a computer, it will doubtless have come with an OS already, I suggest that you learn something about that one first?

Cheers