*)It handles the HTTP protocol.
*)It receives an HTTP request,
*)It responds with an HTTP response, such as sending back an HTML page.
*)To process a request, a Web server may respond with a static HTML page or image.
*)send a redirect, or delegate the dynamic response generation to some other program like JSPs (JavaServer Pages)and servlets
*)It generate a response, most often in HTML, for viewing in a Web browser.
*)It exposes business logic to client applications through various protocols.
*)It provides access to business logic for use by client application programs.
*)The application program can use this logic just as it would call a method on an object
*)It provides Security,Trasaction,MultiThreaidng,Resource pooling ,etc..
A Web application runs within a Web container of a Web server.
The Web container provides the runtime environment through components that provide naming context and
life cycle management. Some Web servers may also provide additional services such as security and
concurrency control. A Web server may work with an EJB server to provide some of those services.
These EJB application used application server which run on application container.
For read in details to visit....http://www.roseindia.net/servlets/IntroductionToWebServer.shtmlhttp://www.roseindia.net/ejb/application-server.shtml