There's a couple things you're going to want to know about Armada II and its overall design (which can on certain occasions be seriously fickle about what it lets you do). It's best you learn the ins and outs of the game's overall design and where things are located before you try to make it better. Otherwise you might only succeed in making things not work at all. 

That's really the first and most important thing to remember about A2 modding: there's nothing wrong with making mistakes. As long as you can correct them. 

And so it begins.

Operating Systems And Armada II

The Tools You'll Need

The Armada II Directory Structure

Planning and Enjoying Your Mods