A sitemap is a list of your website content accessible and available to crawlers or users, it's in format of a Web page that lists the pages on your website, typically organised hierarchically.
Most search engines will find this when they index your site, but it is sometimes necessary to submit it manually. In all cases, the URL of your sitemap is:
You can also access your sitemap through your Google webmaster tool dashboard if enabled on your site. This article will explain how to set that up with your Moonfruit site.
It is not necessary to upload a sitemap file to your site, as the software generates and updates one for you.