I can start you off.
1. 1st copy all the .rez files in the 'C:\Nexon\Combat Arms\Game' folder and put them in a folder called 'original rez' (put that folder in your 'my documents' and never modify them!).
2. Next make a folder called 'Mods' and put all your applications in there (RezInject, RezExtract, DTXconvert, & DTXview)
3. Use REZextract to extract the DTX or LTB files from the rez files in the 'C:\Nexon\Combat Arms\Game' and put them in your 'Mods' folder.
4. Next, conceive of a mod in your head and use the tools to make that happen