When companies first go online, the biggest challenge they face is luring visitors to their sites. It takes advertising, or in todays language online marketing, to get the word out about the site and how to get there. Traditionally, advertising is not cheap and people pay for advertising without any guarantee that it will draw in new visitors to their online site.
With affiliate programs, your advertisement is carried by affiliates who get paid only if their site points visitors your way. They will place you ad on their site and when one of their visitors clicks on your ad, tracking software knows where the latest visitor came from, what they looked at and what they may have purchased. You, in turn, promise that site a certain payment for every sale that was made from that sites visitors.
Using this method, advertisers pay only for results. In order for an affiliate to make money their goal is to produce a lot of sales and they, in turn, advertise their own site. They will also usually be affiliated with several sites at the same time, realizing commissions from every sale made on every site at which they are connected. There are some site that offer nothing...