Understanding AdSense

AdSense is an advertising program that anyone who publishes a Web site can
use to generate income for their Web site. But there’s one small condition —
Google must approve your site before ads are shown on your site.
A longer explanation is that AdSense is an ad-placement program that utilizes
Google’s proprietary search capabilities to determine the best placement for
ads that are purchased through the Google AdWords program.
AdSense is contextual advertising, or ads that appear in the context of surrounding
content. What this means for you is that AdSense ads are related to
the content of the pages on which those ads appear.
It sounds complicated, I know. And really it can be very complicated, but the
bottom line is that with AdSense, you can place ads on your Web site that
are targeted to the content of your site. So, if your site is about Chinese
Crested dogs, ads for Web-based human resources applications don’t show
on your site.
In return for placing those ads on your site, you’re paid a small amount each
time one of your site visitors clicks an ad, and in some cases, even when site
visitors just see the ads.