The XML sitemap is a list of the pages on your website. Creating and submitting a sitemap helps make sure that Google knows about all the pages on your site, including URLs that may not be discoverable by Google's normal crawling process.
The XML sitemap will be generated automatically by cron and the index file of such sitemap will be able by the <your_web_site>/sitemap.xml.
Please follow the Google instructions to submit your sitemap:
http://www.google.com/support/webmasters/bin/answer.py?answer=34575&query=submit+sitemap&topic=&type=