This template allows you to:

Download a prebuilt site to your machine and make changes to the template for updates. You can customize page content to suit your needs and then publish to your host.

Firstly, define a new site in Dreamweaver for the template.
Go to File -> New From Template, and select the Main Template.
The body section has been defined as an editable region. You can make changes here for your new page.
To make "site wide" changes, simply open the Templates/Main.dwt template, and make your changes there for the headers, footers and navigation.
On saving the template, you will be given the option to update all pages in your site with the changes.