IRC's a group chat system, been around for a looooong time. There are dozens of IRC networks, where you can find channels about... just about anything.
You can get standalone IRC clients such as mIRC, clients that handle multiple chat/IM systems such as Trillian, or the Mozilla browser even comes with a better-than-nothing IRC client called Chatzilla.
Basically, once you have your IRC client, you point it at irc.gamesurge.net as the server name, and once it connects you join channel #ppgmod.