Each IRC user has a nickname. All communications with another user is either by nickname or by the channel that they or you are on. To run IRC, you need an IRC program. There are lots of them out there and your internet provider may have already included one in the package. If this is the case, you don't need another Chat program, skip to the next section on How do I Connect.
Most people prefer a simple user-friendly program.
This site also has step by step instructions for configuring the software including instructions for AOL, Compuserve or Netcom users. It is very easier to install and set up. The Consummate Winsock Page provides a comprehensive list of window-based IRC programs which you can download. If you are using MacIntosh, the recommended IRC programs are ircle and Homer. You can download either of those from the New IRC User Page.