The exception means, very simply, that there's no server on port 80 of the local host when the client opens a socket. The line Server s=new Server(); serves no apparent purpose here. I'm guessing that Server is a class that listens on port 80, and this client is supposed to connect to it. If that's the case, then perhaps you should try creating the server before trying to connect to it.
As the previous post states there is no web server running on port 80 for you to create a socket connection to. Because of this the exception is being thrown. Try a different server for example www.yahoo.com etc..