Joining another company's affiliate program is one of the simplest ways to get started with internet advertising. While affiliate links aren't technically ads, they allow you to make money by promoting someone else's product. As an affiliate, you earn a commission each time someone you've referred makes a purchase. To encourage sales, you might post a banner on your site that links to the affiliate site or publish a newsletter article about their product.

Different affiliate programs offer different payout options. Some might offer 10 percent commission for each sale, while others pay up to 50 percent of each sale. You'll want to shop around for the best deal for you and the best fit for your site.

Some internet advertising pros are actually making all their income from signing on with multiple affiliate programs. They don't even have a product of their own! This isn't a strategy for beginners, however, so take some time to check out different programs before committing to this option.

Use targeted advertising with Google AdSense.

Google's AdSense program allows you to make money advertising on your site by placing targeted text ads generated by Google on your pages. The ads appear in rectangular boxes running down the side or across the bottom of a web page with the words "Ads by Google" over the top. These ads are paid for by businesses that use Google's pay-per-click program, AdWords. These ads reflect the content on your site, so if your site sells a book on how to recognize authentic baseball cards, for example, the ads that appear on your site might be for baseball card retailers.

As a Google AdSense publisher, you earn money every time a visitor to your site clicks on one of the AdWords ads on your site. If you're getting a lot of targeted traffic--and if these visitors are interested in the products being advertised--that could mean a healthy new source of extra income for you.

Best of all, Google AdSense is free to join. It's easy, too. Google does all the work of finding relevant ads for your site--you just collect the payments.
A word of warning: Google ads don't work for all sites, so if you add them, be sure to test them. You don't want to lose credibility with your target market.