Basically you can find a lot of information in the /ircintro.hlp which comes with mIRC. (Just type /ircintro). The following however are links to more technical documents which comment on the inner workings of the IRC protocol as a whole.

RFC stands for "Request for Comments" and they are basically an internet standard on how IRC servers/channels should work. This can help those who wish to develop their own IRC client (like mIRC) or create their own IRCd. Compliance with such standards is strongly encouraged but not legally binding or anything like that. More info on RFCs is available here.

For a deep look at the RFC 1459 IRC Protocol :
This document has been extended by the following RFC's (Request For Comments)
RFC 2810:Internet Relay Chat: Architecture :
RFC 2811:Internet Relay Chat: Channel Management :
RFC 2812:Internet Relay Chat: Client Protocol :
RFC 2813:Internet Relay Chat: Server Protocol :
DALnet: #HelpDesk, #mIRC, #MISHScript - Undernet: #mIRC, #mIRC-Scripts