"Please create an account or login on https://www.gog.com
Go to https://www.gog.com/redeem
Enter the code and then press "CONTINUE"
After a short amount of time you will see the details about the product, please press "CONTINUE" again.
Download and install the GOG.com downloader
Login to the software and get back to the product page
Go to https://www.gog.com/account and look for the "Games" tab.
Press the box of the product you want to download.
Activate the GOG.com Download Mode on the right side of product menu.
Choose the installation package from the list and save it with the GOG Downloader."