WordPress.com provides sitemaps for every one of their free hosted blogs. We users do nothing. Yes they are useful and yes Google does strongly suggest they be provided. http://en.support.wordpress.com/sitemaps/
Just to be clear. WordPress.com has already provided a sitemap for your blog. See your Google Webmasters Account. If you would like to create a site index you can follow thee steps in the entry I linked to above.
Every time you copy text using Ctrl C that text you highlighted is automatically copied to “your computer clipboard”. If it wasn’t then when you clicked Crtl V nothing would be copied.