Asked how? A bit c Thread

Greetings to you all,
I've been trying to figure out for a long time how the great mods work when playing, in the descriptions you only ever see a download link, but I'm stumped as to where the stuff has to go and how to start

here for example:

Very nicely done, but when I play it it doesn't look like that.
Can someone reach under my shoulders and help me out of this mess?

Best regards
DAB