What About Affiliate Marketing?

What About Affiliate Marketing is Cool and How Can You Start for Free?

There is a rising trend in one form of making money online and that is blogging for profit. I love this way most. So, What about affiliate marketing is so cool?  How can simply writing words on a website generate thousands of dollars per month of passive income.  How can you get started for free?  Why do I believe this is the single best and most profitable way to earn money online?