Well, you'll need a program for accessing IRC such as mIRC or IceChat (or use the Chatzilla extension if you use Firefox). Once fired up just enter the command /server irc.esper.net to connect to the server.
From there type /join #absolute-community to go into the channel. Once you do get there you'll see yourself listed as a guest. Type /nick followed by the name you want to change to that name.
It's really a very simple things once you have a few of the basic commands.