An affiliate marketing network can help you promote your business by "outsourcing" your salesforce. Basically, an affiliate marketing network is like a person who knows a ton of *great commissioned salesmen who want to sale your product for you.
(Please note that *great is a loosely used term depending on who you work with ;)
Instead of you making posters, going to retail stores & talking to managers for product placement, using Google AdWords, creating banners... you can pay someone else to take the risk & do the work.
You set a price you pay them per sale & they go out to sale your product. Just be careful that you do the math first. There are a lot of online affiliate programs, but if you own a product make sure to do your homework. I have an affiliate program to promote my products online so I know something about the topic.