A server application can communicate through a port, such as a web application can and multiple client communication through port 80, so is an application "and" how to implement and multiple client communication?

1. Here "and" I don't understand is a server application can really and multiple client communication at the same time? Or in fact only one client at the same time to communication and server applications, and because of a single connection communication caused a shorter application server and multiple client "and" illusion of communication?

2. Whether on the level of the socket can be so understanding: application server and multiple clients at the same time is really can do communication, port is equivalent to a conductor, the conductor connection on a board, board has a lot of socket (socket) server, so that multiple plugs (client socket) can be put on a board at the same time, to complete multiple client and a server application communication "and"?

3. Each application can and client communication through a port, so, a large website or im server is how to ensure the stability of the client and server applications, efficient connections?