Can someone help me to understand how to implement this code?

Continuing the discussion from Can Dataview return files that are PDF/Epub, or only .md?:

What I’m trying to do

I am particularly interested in the implementation of: LIST A NON MD FILES AS LINKS

this does exactly what i wanted to do - which is a list of all non MD files in my attachment folder.

Things I have tried

I have no idea what i am doing with the code even though i understand the basics of dataview…