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provide information on several clients from this page, I have not used most of them myself--I rather like my trusty ol' outdated, slightly customized ircII.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!