When you join an Affiliate program and choose the products that you want to sell, sellers provide you with a unique affiliate code that you can use to refer traffic to the target site. Most affiliate programs will offer ready made text links, banners and other forms of creative copies whereby you only have to copy the code and place it on your website to start referring traffic. When interested visitors click on these links from your site they get redirected to the product site and if they purchase a product or subscribe to a service you as the referrer make a commission.
The sellers can track your performance through your affiliate ID and the affiliate softwares that they use. You also have complete, real time access to all sales and commissions stats.