Thousands of people do this because they can start making money almost immediately without the expense and time needed to produce a product themselves. Having a website is not necessary and there is no interaction with your potential customers beyond getting them to the sales page. 

Getting involved in affiliate marketing is a great opportunity to make a lot of money on the Internet, but one should not go into it blindly. As an affiliate you must invest some time in research, this is absolutely necessary. Know what products you want to promote, how much you will make on each sale and the return rate of the product. If possible it is a good idea to buy or request a sample so you know the product inside and out. 

As a first time affiliate it is a good idea to start with reasonably priced products making at least 50% commission. The most critical part of affiliate marketing is of course marketing. The issue of traffic is one of the most central and fundamental issues in making any money online. You can separate your marketing campaign into two distinct groups, paid and non-paid. Free marketing can be quite effective if you know how it is done. Here is a list of the most popular methods for getting traffic for free. 

Article marketing ? A great way to increase your ranking with search engines and direct targeted traffic to your sites. You should write about what you know. If you do not have more information on your topic than does the average reader you should probably choose another topic. Write your article in a conversational tone so that it is easy to read. Do not make your article too long, remember it is an article you are writing not a book. A length of 450-750 words should be ideal. Your article should be informative and about your website topic. If its just useless information your readers will expect the same from your website.