Affiliate marketing is essentially selling someone else's products. There are sites like Commission Junction, Amazon, Clickbank, and more that offer affiliate programs. You just have to somehow offer their products to potential customers (setting up your own website is generally a good idea) and get them to buy. For every purchase made, you get a % of the sale.
Promoting the website using the other websites which work on commissions generated from lead generation.
Affiliate Marketing is recruiting or referring other people to a website and when the person you refer signs up or pay for the program, you get a commission. If you are taking interest in Affiliate marketing then moreniche.com is a great place to start. and if you want to learn how to get a free .co.cc domain and then pm me. But affiliate marketing is a great way to make money and is very simple if you know what you are doing. Research google for information about how to promote affiliates.