cPanel is a common admin Control Panel app.
Anyway, since you're hosting your site on Google, they've done most of the work for you http://www.google.com/support/sites/bin/answer.py?answer=100283&topic=15324
How do I submit a sitemap to Google Webmaster tools?
Once you have verified your site with Google Webmaster tools, Google Sites will auto-generate a sitemap xml file. Your sitemap will be generated at:
http://sites.google.com/a/(your domain)/(site name)/system/feeds/sitemap for Google Apps.
http://sites.google.com/site/(site name)/system/feeds/sitemap for sites under sites.google.com/site
Once these Sitemaps have been created, you can submit them to Google using Webmaster Tools.
Please note: your site must be marked as a public site in order for it to be verified.