This simple campaign is not really intended to be played, but studied as an example of Wesnoth Markup Language. Almost every line of code is explained in the code files themselves. To find the code, use the blue [ i ] icon on the bottom left of the Wesnoth main screen to open your add-ons folder, then open WML_Guide. The code is in _main.cfg, and three other .cfg files in the scenarios and units folders.
Feel free to use this add-on as the foundation of your own campaign!
(Finished and ready to use, but probably could be improved.)