IRC is the devil =)
First you need an irc client, everyone has his or her preferance. Personally I use xchat. Other ppopular choices include pidgin and irssi.
When you start your client, you will be given a list of servers to connect to. Each server has hundreds if not thousands of channels. You then join a channel.
You enter commands in the same box where you enter text, start them with a /
So to manually join a server / channel:
It takes a little while to become comfortable with irc ...