sites

Drupal is award winning, world's best CMS. It's strong, flexible, free and opensouce. Drupal offers web sites a broad range of features such as multi-user administration, community interactivity and news aggregation. There are many other features made possible through contributions from the Drupal community.
  it has been developed to be modular and easy to adapt to almost any situation, it is used by large organizations such as the onion for delivering articles, but can just as easily be used to create web2.0 based applications.

You should have at least one sites defined in your Dreamweaver installation for testing your themes. To define sites click site, new site. An ideal site definition for Drupal theme is like this. Note:- I assume that you have installed Drupal locally.  Else refer these articles 'How to Install Drupal on an XAMPP installation' and 'Installing a Local Web Server'