If you're just getting acquainted with IRC, I recommend taking a look through the General section, particularly the Undernet FAQ (Frequently Asked Questions) list. Then hop on down to the Clients section and grab something suitable for your system, if you haven't acquired a client program yet.
For the really curious
I used to maintain the San Jose Undernet server.
If you're curious, or maybe for a laugh, the Nostalgia
Page contains information about the (now defunct) server.
Who knows, you may even find a nugget or two of useful information there.
For problems using an IRC server, you should mail the admin of that server
if you can't find the answer in one of the FAQ lists.
Problems relating to particular channels need to be worked out with the
operator(s) of the channel or with the
Undernet Channel Service (for
registered Undernet channels). Problems installing or using client programs
should be addressed to the client author or an appropriate mailing list or
IRC support channel. While I try to provide information on several clients
from this page, I have not used most of them myself--I rather like my trusty
ol' outdated, slightly customized ircII.
Of course, your suggestions are always welcome. Meanwhile, on with the show!