The purpose of this dialog box is to specify a URL prefix so Dreamweaver can use your testing server to display data and connect to databases while you work. A URL prefix comprises the domain name and any of your websites home directorys subdirectories or virtual directories.
Suppose your applications URL is www.macromedia.com/mycoolapp/start.jsp. In this case, you would enter the following URL prefix: www.macromedia.com/mycoolapp/.
If Dreamweaver runs on the same computer as your web server, you can use the term localhost as a stand-in for your domain name. For example, suppose your applications URL is buttercup_pc/mycoolapp/start.jsp. Then, you can enter the following URL prefix: http://localhost/mycoolapp/.