Hide all windows Mac OS
As far as I know, the main way is just to "push" all of the windows off the desktop with the F11 key leaving only the desktop visible.
As per the Apple Support pages here there are three possibilities:
Show the desktop (hide all open windows) via F11.
Use Command + Option + M to minimize all open windows [to the dock].
Use Command + Option + H to hide all open windows except the one in focus.
As others have said, you can't hide the Finder environment (without modification).
As far as I know it's not possible. Mac OS must have at least ONE application with focus, even it must have ONE application running.
As a test, you can enable "Quit" menu option in Finder (http://osxdaily.com/2010/02/12/how-to-quit-the-finder/). Just login in "safe mode" (pressing SHIFT just after login in. In this way none application will be running except Finder. After quitting Finder, it will re-born automatically. It's the same concept to hide all applications. At least one (Finder at least) will be the focus application.