The Site Definition wizard has three sections to help you set up a Dreamweaver site: Editing Files, Testing Files, and Sharing Files. Each section might have multiple screens depending on the settings you select. At the top of the dialog box, the bold section name indicates where you are in the setup process. You might not need to set up folders in all three sections; the wizard questions help you determine your needs.
The purpose of this dialog box is to name your Dreamweaver site and specify its URL.
Dreamweaver uses this address to make sure site root-relative links work on the remote server, which may have a different folder as the site root. For example, if you are linking to an image file on your hard disk in the C:\Sales\images\ folder (where Sales is your local root folder), and the URL of your completed site is http://www.mysite.com/SalesApp/ (where SalesApp is your remote root folder), you should enter the URL in the HTTP Address text box to ensure that the path to the linked image on the remote server is /SalesApp/images/.