Well, the 3D desktop, known as compiz, typically gives you wobbly windows and such like. Things like the cube are additional features you can turn on. Have you got wobbly windows?
IRC is Internet Relay Chat. It's like group MSN, if you like, but the original proper thing
You start up an IRC client, which would probably be Xchat, but it might just be down as "IRC" under Internet on the Applications menu. You choose a network to connect to.. there are many, e.g efnet, dalnet, ircnet, freenode. The one you want is Freenode as that's where all the open source projects have their chat channels.
but before you can talk on many of those channels, you need to have registered your nickname with a password, which you do after you connect to Freenode with your IRC client, but before you join a chatroom ("channel").