The purpose of this dialog box is to indicate whether you are building a web application. A web application is a collection of web pages that interact with the user, with each other, and with various resources on a web server, including databases.
If you are building a web application, you need to select the server technology running on your web server.
You can use Dreamweaver to build web applications using five server technologies: Macromedia ColdFusion, ASP.NET, ASP, JSP, or PHP. Each of these technologies corresponds to a document type in Dreamweaver. Choosing one for your web application depends on several factors, including your level of comfort with various scripting languages and the application server you plan to use.