UPDATED VIDEOS:
This is my structured guide through these files.
https://youtu.be/JJMCTyoOYOo
This goes over how to add a Custom Area and NPC for a Black Market trader
https://youtu.be/bBqTstYZBws
UPDATE: on 1/27/22, the Expansion team updated where some of the files are located. Items like the trader.map file and the traderzones are moved to \mpmissions\dayzOffline.chernarusplus\expansion
TheWomberchomby's Video on Expansion Trader implementation.
https://www.youtube.com/watch?v=xwqJ0nIiYb0