Here are a few commands that you may find useful.

/nick New_Name
This command would give you a new nickname of New_Name, so it's best if you replace that part with something else.... hehe

/me
This will change the way your message looks in the Chatroom, Instead of looking like this :-
<New_Name> thinks it's time for a beer...
It will look like this:-
* New_Name thinks it's time for a beer..

/list
This will open a new window within mIRC that shows all channels (rooms) on the server (unless the person who made the room has it hidden of course) then all you have to do is double left click the room you want.

/whois Nickname
This will give you any details the server holds about the person with the name Nickname most of which will be of no use to you at all... :P

/whowas Nickname
If the person with the name Nickname logged off before you had a chance to /whois him/her, then this is the command you need...

/join #Feesch_Trivia
This command would make you join another channel with the name #Feesch_Trivia, if the channel already exists (which it does) then you will just join it... if it don't then you will create it making you the channel owner and giving you op status...

/part
This command will make you leave the channel you type the command in, you can of course type it in one channel to make you leave a different one by typing in the channel name after the command ie:- /part #Feesch_Belching, but why make it hard on yourself....

/quit
This does exactly what it says on the tin, it makes you quit the server...