Step 1: Short Intro About IRC
I.R.C. is short for Internet Relay Chat . From the name it's obvious what it is. This is how it works (today anyway): You download a program that will enable you to use I.R.C., this is called an I.R.C. client. The client asks you to select a server of your choice. Once you have connected to that server, you have the option to open up a channel list (a list of channels in that server) either with a text-based command, or a button (depending on the user interface of your client). You may connect to one (or more) channels and chat with the other users in there. You may want to search around for the list of commands as they can be useful to you yourself in the future, but for my purposes this is optional, as I'm only telling you how to add I.R.C. capabilities to your website.
Also, before I forget, you need a little bit of HTML knowledge for this to work, otherwise you wouldn't have any idea where to stick the code (to be explained).