5. What are promo and gift codes? How do I redeem them?
Promo codes are special “coupons" that can be exchanged for either one, or many free games - depending on the code. They are typically provided via contests or promotional emails, so stay tuned, visit GOG.com often and maybe you'll score a code or two ;).
Gift codes can be purchased by selecting the "Select to gift this order" option, during checkout. You can either send it directly to the recipient, in a GOG-made e-mail, or send it to yourself, and then forward or PM it to someone. If the gift recipient already owns some of the games within the gift, these games will remain in that gift, and can later on be redeemed by someone else. Otherwise, all games not currently owned by the recipient will be automatically added to their account.
To redeem either of these codes, go here