Almost any business that sells goods and services offers some sort of referral/affiliate system. If you look at the bottom of most websites, you will see a link for "webmasters" or "affiliates", click this link and the company will provide you with a special link that is specific to you. When a consumer clicks on your link and is taken to the companies website and buys from that company, your link is tracked and the commission for the sale goes to you. Check out Amazon.com's program it's one of the largest. There are 1000's more though!
The better you learn and understand SEO and the more strides you take to learn this seemingly confusing and complex discipline, the more likely you'll be to appear organically in search results. And let's face it, organic search is important to marketing online. Considering that most people don't have massive advertising budgets and don't know the first thing about lead magnets, squeeze pages and sales funnels, appearing visible is critical towards long-term success.
Can you make money with affiliate marketing? The short answer is yes, affiliate programs can earn a extra money and even a full-time income from home. The long answer is a little more complicated. Like any home income venture, success comes not so much from what you choose to do to make money, but whether or not you do what needs to be done correctly and consistently.