The title is pretty self explanatory. You must have a MCR (My Coke Rewards) account (Amazon account too - Duh!) and it says limited to one offer per account (MCR & Amazon). The code is delivered by e-mail.
The $1.00 "cost" I entered is based on approximately $1.60 for a 20oz bottle of Coke for 40 MCR points so 25 MCR points is about $1.00. If your cost for a 20oz Coke varies, then the effective cost of this offer varies as well.