The concept is basic, you refer someone to a site, they buy something on the site, you may a percent of the sale. You are only paid when you refer a sale or a desired action.
To sign up for it:
- Sign up for a Google Affiliate Network account with your AdSense Publisher ID.
- As soon as you're approved for Google Affiliate Network, sign in and apply for advertiser programs.
- Follow the instructions to start displaying cost-per-action ads.
Some are skeptical and some are eager to try out this old but yet new revenue and advertising model from Google.