Affiliate Network Definition: An affiliate network acts as a go between or middle man between companies that want to advertise their products or services and affiliates like you who want to get paid for refering people to those companies. Companies or businesses that have a product or service to sell will already have a website and payment platform, and affiliates may already have a list of potential customers that are ready to buy that product or pay for that service.
As an affiliate you can place advertisements and banners on your website if you have one or you can use other advertising methods such as google ads ( or other network ads), article marketing and email marketing to send customers to the companies website or offers. So you don't even have to have a website to make money from affiliate marketing.
While some companies and networks will pay a percentage commission on each sale (PPS) there are some companies that pay on a CPA ( cost per action ) basis. There are some affiliate networks which specialise in CPA. Sometimes the action needed from the visitor is as simple as enter an email address. In that CPA example you get paid a certain amount every time someone enters their email address on a CPA form or squeeze page. The payment you receive can be anywhere from a few pennies or cents to a few dollars or pounds, depending on the offer. Usually the steps the visitor has to go through or the more information they have to give, potentially the more you can earn as the payments will tend to be higher. Some CPA offers can be a survey for example. A company might want to gather information on product or service or the people who would use it and in order to get that information they will pay CPA affiliates to get as many people as they can to complete the surveys so that they can gather as much research information as they can. Later that company can either create a product or service to match the audience or improve their product or service or even market other similar products and services to them depending on the the answers they gave when they completed the survey.
There are several popular CPA and affiliate Networks. Neverblue and Clickbooth are two popular networks for CPA and Commission Junction and Linkshare are popular at the time of writing this for PPS. But there are many new affiliate networks popping up all over the net right now.