Affiliate marketing is a form of marketing, in which publishers (affiliates) instead of being paid in advance for advertising space (traditional advertising) are rewarded for actions that are made by consumers on the Internet.
The system is known as "performance-based marketing”, because the person who promotes a website takes his money only in case he succeed to convince the visitor to access the destination site with the express purpose of acting in any way.
Affiliate systems are composed of two entities: suppliers (online stores or advertisers) and affiliates (publishers).

We can talk about affiliate marketing when a publisher (blogger, portal, website, etc.) send a "visitor" to a site that sells a product or service and that guest act in any way on that destination site (buy, sign up a newsletter, etc.).
How it works?
Suppliers create a campaign in which they decide what action they want to make visitors (eg buying a product or enrollment in a newsletter), and the percentage or the amount they lend to affiliates. Then the system loads in different affiliate promotional tools (advertising).
Affiliates enter their sites and apply to campaigns suppliers. After being accepted to have access to all suppliers and promotional tools you can use any combination to generate more conversions.

Affiliate marketing is closely related to e-commerce market. For affiliate marketing to work you must have a basis in this area and serious shopping experience. Any promotion is useless if it makes affiliate stores treat their customers badly.
Then, even more important is that publishers needs to understand the idea and make promotion, not advertising. Advertising is to put a banner about hotel reservation on a site that makes mobile phones reviews. Promoting means that you need to convince your visitor that he must buy that product from that store.

An example of affiliate marketing
An online hotel reservation system offers 5% of the price of the reservation to his publishers. An affiliated publisher with this hotel is a travel portal. If a visitor clicks on an ad of that hotel and then continue to make a reservation at a hotel, then the travel portal will receive 5% of sales.
Affiliate marketing began seriously in 1996 when Amazon launched its own affiliate program. There experienced publishers gather tens and hundreds of thousands of dollars in revenue. There are specialized sites, such as Like.com, which are all model-based affiliate marketing business