How to mod(where do I start at) PLZ HELP ME

I have a Jasper xbox with a 120gb hard drive and my dashboard is 16767. What I wanna know is what do I do to begin modding my console so I can mod mw2 ground war online and possibly gta 5?? Also what kind of mods can I do to this model?? PLZ HELP ME!! Thanks!!
BTW my Xbox GT is
BLG JOJO X