Press “Download”, then run the installer and follow the steps.
Login to Origin with your account or create a new one.
Press “Origin” on the top left Menu of the main window and then “Redeem Product Code…”
Insert your key into the field and then press “Next”. Follow the steps, after a few moments your key will be activated and you can download your game.
When the download is done you can go to your “My Game Library” on the left side menu, left click on your game and then press Play!