Before I tell you the why, I am going to get you to do something here. If you haven't done so already, go grab yourself a GoArticles.com account (it's 100% free).
http://www.goarticles.com/cgi-bin/signup.cgi?submit-member=New+Member
Now for the why...
By signing-up to goarticles.com, you are gaining the ability to post articles on their website. The reason this is really powerful is that they have spent a good deal of time, money and resources on getting their site ranked high within Google and other search engines.
By placing your content on your site you get to benefit from their hard work. You get to get listed under keywords that would typically take months, if not years to naturally SEO into these search engines if you tried to do it with your own website.
But why would they want you to post content on their site? Because they get paid from ads that run along side your articles.
So how do you earn money from your articles?
You earn money from your articles by making recommendations to products via your affiliate links. Remember when I got you to sign-up to one of the 6 affiliates within the second lesson? This immediately gave you access to programs to promote.(After you ordered one of the ebooks or became an affiliate with Global Domains International)