The single most useful command
. It closes your connection
to the server
and, depending on your client
, might close to whole client as well.
Has a simple syntax:
/quit bye bye everyone!
This command leaves "bye bye everyone" as your last words or as the reason for quitting and other people on channel
see it in the end of the line telling about your quit.
It is the only command you'll actually need, though you'll probably be too addicted to use it.