Your income is generated both from clicks on ads and from impressions (number of times the advertisement is shown on your web site).
Besides the clicks and the impressions, you can earn money by including a Google search box in your web site code. If your web site visitors use it you will get a percent of the profit relevant to their search terms. AdSense for Feeds and AdSense for Domains are also available . The first one places ads in the feeds managed by Google for your web site. The second one allows advertisements to be included for domains that do not open a web site with content.