Google has help and services for Webmasters. Among the things they provide and encourage are sitemaps. However, it’s not as complex as it all seems. WordPress and coppermine, and many other CMSs have scripts that generate these sitemaps. There are tools that run from your computer too, but these can’t know the internal structure of the site database, and so they are inefficient or don’t work for dynamic sites like WordPress and Coppermine.
Sitemaps tell google about the content of sites that have dynamic content. You can find out more about services for Webmasters at google. You will need to log into an account to see these pages, but accounts are free.
You will want to look at this page to find plugins or programs to build sitemaps for your site. For example, there is a plugin for WordPress to build sitemaps – WordPress Sitemap Plug-in.