It is a free program that empowers online publishers to earn revenue by displaying relevant ads on their blogs or websites. It comes in a form of text ads or banner that you can place on your page.
These are companies that will pay you every time you generate a sale for them by placing their ads.
Here are some companies that offer affiliate advertisements:
To earn decent income from these methods you will need to generate more traffic to your site. The more people that visit your site the more chances people will click and purchase from your ads.