problem in creating an advertising site..

hello every one i've got an project for my final year and i hope u guyss can help me.

I want to create an advertising site but the problem is that I can't find the way how they operate. They place a piece of code on the website and then they randomly rotate the ads.

My question is how they tract the impression from that piece of code... A little abbreviation is greatly appreciated...

I've have copied some advert code from site

<!-- BEGIN Ad Tag -->
<script type="text/javascript" src="http://syndication.exoclick.com/ads.php?type=468x60&login=subhomoy123&cat=472&search=&ad_title_color=0000cc&bgcolor=FFFFFF&border=0&border_color=000000&font=&block_keywords=&ad_text_color=000000&ad_durl_color=008000&adult=1&sub=&text_only=0&show_thumb=&idzone=681589&idsite=235181"></script>
<noscript>Your browser does not support JavaScript. Update it for a better user experience.</noscript>
<!-- END Ad Tag -->

Can u plz help me with it...

Thanks in advance...