Sitelink extensions are manual AdWords ad extensions that show text below your ad that is clickable and directs traffic to a specified landing page. The landing page differs from the URL listed in your text ad. There is no additional fees; it costs the same rate as clicking on the main ad. Sitelink extensions are ideal for clearance pages, related products or services. They are visible based on ad rank and add value to your ads.
Callout extensions are another kind of AdWords extension, that can help encourage clicks on your ad. Learn more about them in our post on Callouts.