a) I can't see how this is a Twisted Web Question (check the subject)
b) I'm assuming that since you want to write an IRC client you'd have some inkling of what a channel might be.....
Below is a piece of code from ircLogBot.py in the examples section of the Twisted release.
It makes reference to a "channel" - What is a channel. I assume that "sys.argv" when passed into main() must be a "channel"