To play alone, just launch it. Tilt your computer to control the paddle. To play with a friend, make sure both of you are in the same local network. One of you has to start his copy of Pong, and the other should start his after 5-10 seconds... No other setup needs to be done.
netPong looks for an opponent the first time it's launched.... If none is available, it creates a server. The next netPong application that is launched will connect to it, creating a two player game. That gives the system opponent randomness, so every time you launch it, you might get a random opponent.