where exactly do i put mine in? i cant find anywhere in the game menu. please help!

It should say where to go on the slip with the code on it.

Ps3,360 or pc ...which are you playing on?

If you bought yours from Gamestop, and you purchased it for the Xbox 360:
1) Hit the "Guide" button (Big silver one on the controller.)
2) Scroll over to Marketplace.
3) Click redeem code.
4) Type it in!