I'm in the process of writing a complete guide for adding a planet so hang tight for a while and I'll post it in the guides section.
Timbab.... Havent used treEx since the SIE came out.... if I put that somewhere (tho I don't remember), It was probably force of habit (sorry Sytner
As for a tre manipulation guide, I can write one but your probably better just using the SIE making a few folders to practice with and diving in. Unless there are specific files you need to extract for a particular purpose, just pick different types of things and extract file chain (right click or from the menu), to see what gets pulled to your new folder.
For example, pick a weapon...say T21 rifle. Find it in:
object/weapon/ranged/rifle/ and extract the chain to your folder.
It'll pull all the files the game needs to make that weapon work. Try the process for different objects you get in game, say clothes, furniture...in fact anything you see while your walking round in-game. Then try to find the corresponding Lua script files in the server files. Objects follow the same (usually) file path as the tre files. So for the T21, go to:
/bin/scripts/object/weapon/ranged/rifle and you'll find the rifle_t21.lua file.
Practice using it.... delete what you extracted....practice some more. Get used to using it. Maybe try and follow the guide to adding the Barc speeder to pre-cu.
As Timbab says, the SIE is by far the most user friendly and useful tool we have ever had (thanks again Sytner), so your starting to learn at a very good time.
If you get stuck on something then ask questions..... Even better join the MTG irc channel..... Myself or someone will always answer and questions you have. It might not be immediately unless we happen to atk so stay logged in and check every now and then.