(via blog.flip-edesign.com)
A basic Varnish installation consist of Varnishing sitting in from of your web server (referred to as back-end), clients will interact solely with Varnish and never know there is a back-end web server (nor should they have access to the back end directly). When a request comes in to Varnish for a page that is being cached over a standard HTTP connection Varnish will either service this directly to the client (without sending a request to the back-end) from Varnish’s cache if exist or if not in cache will send a request to your web back-end over its TCP socket via an HTTP request...
