Fair warning - this article is not meant for experienced website publishers. This article is meant for those new to the industry. The ideal reader of this article will have a website they made without a plan ahead of time. The website could be a personal site like a blog, or perhaps a fan site, or any site really that people typically make and then one day realize "Hey, I could make money with this." The only type of website that wouldn't really be appropriate with this article would be a site made to compliment an existing service business. The reason is in those cases the website is not supposed to make money, it is supposed to generate interest in your business.
So if you have a content site and you wonder, "Could I make money with this?" Read on.
The easiest way to monetize a site is to join an ad network and put up ads. This isn't as simple as it sounds though. Some sites are better suited to certain ad networks than others, and some sites will have problems getting in ad networks at all.
There are two major types of ads provided by ad networks, those that pay every time someone clicks on an ad (called CPC or cost-per-click) and those that pay every time someone views an ad (called CPM, or cost-per-thousands impressions). A $1 CPM ad will pay you $1 for every one thousand page views. I know that can be depressing if your site only gets a few thousand page views per month, but that's the truth of the online ad industry. A $0.25 CPC ad will pay you a quarter every time someone clicks on your ad, which sounds like it could be better than CPM, and it can, but you'd be surprised how infrequently people click on some ads. Especially when you consider advertisers who want branding sometimes design an ad that doesn't encourage clicks whereas ads that get clicked a lot (such as flashing error box types) are never sold on a CPC basis.
Depending on your site's topic and demographic one type of ad will perform better for you than others. For instance teen sites tend to have poor click through rates and they do not attract high CPC ads so they do better with CPM based advertising. Also forums tend to have poor click through rates so with those CPM advertising is best. A site about building a personal credit history however could command excellent CPC rates and get a good click through rate if they found CPC ads tailored to their content. The easiest way to figure out what ad type will work for you is to try them both. Try multiple ad networks and multiple ad types until you find something that works for you.