Basically, you pick a profitable niche for your online business, and then you find an affiliate partner who has products available in that niche. Some of the most popular affiliate sites are Clickbank.com, Amazon.com, and CJ Affiliate by Conversant (formerly Commission Junction). Between them, they offer just about any digital information product (like ebooks, audio files, video files) or physical product you can think of. May big name companies and brands, like Wal-Mart, Home Depot, etc. run their affiliate programs through these third-party affiliate sites.
One of the most important internet marketing strategies is to develop every customer's lifetime value. At least 36 percent of people who have purchased from you once will buy from you again if you follow up with them. Closing that first sale is by far the most difficult part -- not to mention the most expensive. So use back-end selling and upselling to get them to buy again: