XML and LUA are game codding languages. XML is the main code used to mod. Look around a bit and you'll find some good XML Turtorails. As for LUA, oddly some people find it challanging and confusing. I know of no tutorails for LUA. If i find the motivation, I'll find something to LUA code and post a tutorail on it

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As for mapping, yes, it means making maps. It's probly the second easiest thing to mod, the first damage numbers and what not in XML. However, the question is: How good can you map?
If you even need anymore help, post it in the "Modding Help" section, Ok?