Private message - /msg nick message
Sends nick a message.

Nickname change - /nick newnick
Will change your nickname to newnick.

Ignore a user - /ignore nick
Will ignore user with the nick nick.

Unignore a user - /ignore -r nick
Will unignore a user with the nick nick.

Performing an action - /me actiontext
/me does a little jig will show as: * Nick does a little jig

Joining a channel - /join #channel
Join channel #channel.

Parting a channel - /part #channel
Parts channel #channel, if the #channel is omitted the current channel will be parted.

Listing channels - /list searchtext
Will list all channels matching searchtext, if no searchtext is entered, all channels will be listed.

User information - /whois nick
Displays the user information of nick, see also /ns info nick.

Leaving/Quitting - /quit message
This will disconnect you from the chat and send an optional quit message to the server.

Message Of The Day - /motd
Displays the current Message of the Day (motd).

Switching servers - /server newserver
Disconnects you from your current server and connects you to newserver, very handy to find the server you have the best connection to.

mIRC Help - /help topic
Opens the mIRC help file for topic. This will only work for the mIRC client.