One thing I would really appreciate any clarification on: How did they create the virtual desktop that the mouse and keyboard could interact with as if it were

One thing I would really appreciate any clarification on: How did they create the virtual desktop that the mouse and keyboard could interact with as if it were a physical screen off to the side? Edit: Wow @pcouy, thanks for the sub 2-minute reply! Cheers~ and kudos to you for creating a fantastically easy to read and entertaining writeup.