got my game from gamestop how do you download the bonus stuf

You should have a code from them, if not, contact Gamestop.

If you have a code, you can do it from your Xbox by pulling up the guide and going to Redeem Code.
Another way is by going to Xbox.com and signing in. Then, go to My Xbox, and Redeem Code.

The code from gamestop for me was printed on my receipt.

I'm still having problems with my code. It does not work at all. What's the deal?