macOS, in its current incarnation, started out as a derivative of NeXT's OPENSTEP operating system, rebuilt to resemble the classic Macintosh operating system. The previous system was known simply as "Mac OS System 9", being the ninth major version.
Using PC keyboards
When a PC keyboard is connected to a Macintosh via USB, the Windows keys act as the Command keys and the Alt keys act as the Option keys. The positions of these keys are reversed from the Macintosh standard, with PCs having the Alt keys innermost.
Within System Preferences, under Keyboard or Keyboard & Mouse (depending on system version), you can remap the modifier keys, and thereby swap Option and Command.