I was wondering could you help me I have been trying to figure out what tools to use to do what and where different information about the game is kept

I have read the tutorials but there is a lot of stuff that I still do not get like:
1.) What is all these files that I got when I decompressed the PCK files? what relevence do they have to the game?
2.) I also have an XML editor (Peter's XML Editor) but I have no idea what I use it for or how to use it.
3.) I am trying to put another subcategorie into the trade menu but I'm not sure which tools to use to do this and where to put the file, once I have done this.
I know how to get to the script editor in-game (type "Thereshallbewings")
so I have been trying that but no luck so far

Plz can you help me I know I sound stupid, but I have modded games before but this one goes right over my head. I feel like I'm in a windtunnel

