After purchasing an EA related Product.  You'll receive a cd key in the mail. 

Before looking at your email head on over to http://www.origin.com/us/about and select Download Origin.

While it is downloading head on over to http://store.origin.com/ to make an account if you haven't already yet.

Install Origin.  Login with your account or the one just made.

Then After loging in select the icon in this image.

Select Redeem Product Code as shown in the image.

Input your code.

Select Next.  Then Walah it'll verify and you can download the game in your "MY Games" tab. All done!