This is what we have all grown up believing since the dotcom got associated with stories of riches. Get the eyeballs, advertising will follow and you can live it up. This is how all media survives. If you have the audience, advertisers cannot ignore you.
The simplest way to start is to sign for a service like Google’s Adsense. Acting as a middleman, Google approaches advertisers all over the world and automatically places ads on blogs and sites that sign up with them. The advertisement that gets displayed is contextual to the content on the site, and it is all done automatically.