To open the file is quite simple, any notepad can open it, it's just a .txt file with another extension. However, I would recommend an editor like Notepad++, which has features to help on coding.
I searched this forum for tutorials too, but didn't find any
What I did was to start opening the files, changing things in there and seeing what happened in the game etc.. There is also a Menu.doc file in the menu folder, with some info on the functions, but veeeeeery very crude, it's hard to understand even, especially if you don't know much about coding. But if you do, you may understand it by trial and error