learn affiliate marketing
Affiliate marketing is a business partnership between online marketing individuals or companies (affiliates) and the actual front end businesses (merchants). A user will land on an affiliate site and click through to a merchant. The merchant will track the user and if a sale is made then the affiliate will be due a commission, which has been set by an agreement. Many merchants operate through 3rd party tracking software like Affiliate Window, who manage the relationship and pay affiliates the commission due.
Many people on the web run blogs that discuss affiliate marketing with tips and tricks on how to get started. Some examples would be CPA networks and Free Adwords.
As it is a long learning process, start with a small niche and a small website to get used to setting up an affiliate site. As you learn more, you can then set up multiple sites or blogs, to expand your offering. For blogs talking about this subject go to Affiliate marketing blog and Affiliate Stuff.