Yeah, Kat or I can give it a shot.
Oooh oooh oooh I just started using this when some friends made a channel for this game we play.
On the first screen that pops up, on the left are all sorts of neato things to change and customize, which you can fuck with later. The main one is "Connect".
The only crucial things on that first screen that pops up ("mIRC options") is IRC network..which I recommend to be on "All", and just below that is the server. Of course there are tons of servers...the ones in the pulldown menu are the most popular I suppose. So, choose one..or if there is a specific one you were told to go to you can enter the info for it by clicking "Add" and filling in the stuff.
And of course there's name and email address..nickname is the most important one. After you choose one, depending on the server, you can register a nickname with a password so that only you can use it. Sometimes servers use "nickserv", others use "authserv". Ex: DALnet I know uses Nickserv, and Gamesnet uses Authserv...both slightly different but do the same thing.
For nickserv:
/msg nickserv register <password> <e-mail>
to register your current name, and subsequent times when you log in, put:
/msg nickserv identify <password>
Just an example. And if these commands are old, you can, once you connect to DALnet, type /nickserv help and it will tell you a bunch of nice things.
For gamesnet, it is different...when you log on to their server they give you this URL for important shit:
http://www.gamesnet.net/guide.php That shows how registering your nickname is server-specific. And
:: points :: it tells you how to do stuff on that site.
Also, if you see several different DALnet servers, or for gamesnet there is an east and west server...they are the same network, just different machines to connect to. So if you register a nick for DALnet, it is for ALL of the DALnet servers listed there.
You can do PMs on mIRC just like AIM. Just remember that when someone PMs you in mIRC it appears on the second bar from the top of the window, just below the first row of buttons...and the window doesn't jump up at you like in AIM, so,
pay attention to that (if you want..usually I just close those PMs since there are bots out there that mass PM people with junk).
:: teeters out :: Hope that helped.
mIRC,Irc or WHATEVER... 
(she did help me quite some when I was a nOObish
).
