I was pretty confused at first!
It's pretty easy once you understand, basically download which ever modmenu you want, example; Jiggy Modmenu v4.5.
Firstly you will need the TU18 update, you can download it from here or google it.
also you will need the modded default_mp.xex and Tesseract.exe as well
Once you have all them files including the patch (modmenu) you want to use, download black ops 2 to your HDD
(Use a USB or Xbox Neighbourhood)
Move all the files from the TU18, then move the Tesseract and default_mp.exe into your BO2 folder, once that is all done and moved over, create a folder called "Raw" and inside of that folder just move over your patch (Maps foler) and there you go, just press default_mp.exe and it will load up the game (multiplayer screen) click on local or systemlink, start the game!
If you're able to move, press LT and Knife! HEY PRESO you have jiggy modmenu.
if you'd like to change the patch, simple delete the Maps folder and replace with your other patch (maps folder) and there you go! another patch, or you can make copys of your jiggy modmenu (re-download the game and change the maps folder with whatever!
I have 9 copies of BO2 on my HDD, purely so I can just load up the patch faster! even though it's just copy and pasting!
Hope this helped, if not PM me and I'll try to help you!