EADM you need to click the sign in tab, after that go to activation, from there you can put your codes in from your games. Once you put in the code the game will show up in the tab that has your user/email address across the top. Click on start and then it will download. Once that is done, you can install. But you have to activate the game to be able to use it. Hope that is a better explanation. I'm rooting for you!
EDIT: I just remembered that I updated my EADM, now it looks different. If you have the new one, it will pop up with the log in screen. Log in. On the right side of the EADM there is the a little tool/gear, click on that. Go to redeem game code. That is where you put in the code. Once it is accepted, your game should show up in the list. If not, click on the tool/gear and choose refresh my games. Then you can download and install from there. Sorry if you saw the above post and got confused, I just updated my EADM last night and completely forgot they changed the layout.