Here's how affiliate marketing works: When you join the company's affiliate program, you get a special tracking link from them. Then, you'll place that link within posts on your blog, emails to your blog subscribers and weave it in elsewhere that you reach your readers. When someone clicks on that tracking link and completes a purchase, sign up (or occasionally another metric), then you earn either a set fee or percentage of that sale. You're getting compensated for referring new customers to your affiliate partners. My roundup of Bluehost reviews is a good example.