Explain to me...how google script work?
Here is a typical adsense script:
<script type="text/javascript"><!--
google_ad_client = "pub-xxxxxxxxxxxxxx";
/* 468x60, created 9/23/08 */
google_ad_slot = "2846379014";
google_ad_width = 468;
google_ad_height = 60;
//-->
</script>
<script type="text/javascript"
src="http://pagead2.googlesyndication.com/pagead/show_ads.js">
</script>


How can those simple lines of code can do wonders on your site? How do they know what ads to put on?