When you create a site, you always begin with a template. You can also derive templates from sites you create.
A template is a fully designed page or site that you can use as a starting point for your own pages or sites. A typical template might include a banner and navigation buttons, an assigned SiteStyle, and text or other content. You can start a new site from a template or insert one into your current site. Once inserted into a site, you can modify template pages any way you like. Templates are described in detail in Working with Templates.
You can also open an existing site and add to it, change its style, or modify it.