This is helpful but the latest version of the diagram tool is a bit different, isn't it?
My method is to paste the game FEN into ChessCat and work-out my variations. Then I copy the pgn from ChessCat and paste the pgn into the diagram tool.
ChessCat is a very nice (and old) pgn reader which is a great analysis tool.
However, some people report difficulty installing it on their PC.
http://www.chesscat.loncarek.de/download.html
If you copy below to your group, please give credit to @huntwabow and club Lotus