OK, you've learned how to write and you've practiced and feel comfortable doing it. The next step is to start selling what you write! There are different ways to go about this, so I'm going to break it up over a few posts. Today I'm going to focus on online content sites.
Online content sites are websites that are like big article warehouses. They pay you a pittance for putting your article on their site, and they earn money from the ad revenue. These sites include Associated Content (they pay a small up-front payment plus $1.50 per 1000 page view residuals), Helium (they only pay residuals on some mysterious formula related to the subject, page views and where you're ranked), Demand Studios (they pay $15 up front for article ideas they suggest and they just changed how much they pay for subjects you suggest so I don't know. No residuals), and Suite 101 (they pay a revenue share of the ad income, which is pretty good). There are others, like Textbroker, Triond and eHow, but I have only used the ones above.
There are other places to earn online; you just have to keep your eye out. letterrep.com is a place where you can write letters for people, and you get paid $10 for every letter you sell. I've sold a few there.
The big thing to look out for is that if they charge you money to sign up and get work, it's probably a scam. Many places that charge a subscription fee just to view job listings have very few listings, and what is there gets snapped up quickly. These places are likely to then bombard you with spam or sell your information to add insult to injury.
The forums at Associated Content and Accentuate Writers have some job listings you might find helpful.
Posts to look forward to: SEO work, bidding sites, magazine work, how to write a query letter