This is one of my personal favorites so odds are you initially got to this guide or one of my many websites via article marketing. The gist of article marketing is that you write articles on a given subject and allow websites to republish it royalty free given that they do not change the contents (similar to this guide). Since no author would do this for free, you are typically given a slot to put 3 links back to your sites. The catch is that you cannot directly link to an affiliate product, you need to send them to sites you own first that contain the links.
Writing articles isn't as hard as it may sound, I can typically write a high quality article in about 6 minutes and I'm a computer science major, I shouldn't even know how to spell article. Typically you will get accepted as an author by all the major article directories.
To actually get a good number of backlinks and promotion out of your articles it is essential that it is submitted to multiple placed. To do this I typically submit manually to www.ezinearticles.com and then pay $1 per submission from iSnare to have it distributed to over 40,000 publishers that are looking for content on their sites.
The only way to succeed with article marketing is to make sure that many different places receive your article, and I typically use two methods for this. First I use iSnare's Distribution Service, and then I use software that I bought called “Instant Article Submitter” which submits my article to hundreds of directories automatically. For more information on Article Marketing I recently created a page dedicated to what it takes to succeed:
http://www.affiliatemarketerguides.com/articlemarketingguides