Here is a brief list of commands that will help you communicate with other players:
[channel] <message> Send your message to channel [channel].
[channel] :<emote> Show emotion over channel [channel].
[channel] ;<emote> Use preformatted emote <emote> over [channel]
channels See what channels you are registered on.
ping <player> This will produce a sound at the other player's computer. It means: “Are you there?”
pong “Yes, I am!”
say <message> Say something. All the people in the room will hear you.
'<message> Same as 'say <message>'
emote <message> Perform an action into the room you are in.
:<message> Same as 'emote <message>'
tell <player> <msg> Sends a tell to a player.
whisper <player> <msg> Whisper in somebody's ear.