Seperate server - client

Hey everyone,

Im going to make a Multiplayer game and read the network tutorials here:http://unity3d.com/support/documentation/Components/Network%20Reference%20Guide.html

But I think theres not described how to create a seperate server, so not that a client is the server and client at the same time, but a central server where all clients have to connect to and synchronizes the states. I think I need a seperated program for that or how that is going to be?

Hope someone can help me, thanks :)