People in the same room as you can of course hear whatever you "say" there.
They can obviously not hear whatever you "whisper" to a specific player in
the room.

You can communicate with people who are not in the same room by using the
"tell" command. You can also communicate with a group of players by using
a comms channel.

There are 2 comms channels available to everyone:
general and sales

You connect to a channel with the comm connect command,
you can disconnect again with the comm disconnect command.

You can use comm auto to automatically connect to a channel
at login.

Sending messages on a comms channel is done by entering [
, so '[general hello' would make you say hello on the general comms channel
Note that you can abbreviate the name of a channel to the first letters that
uniquely indentify that channel, so [g will usually be enough for the general
comms channel.

You can emote to a channel by using ] instead of [ and you can use soul
commands on a channel by prepending them by a ! (for example [g !smile )

Available channels for all players:

general : General talk, does not have to be in character
sales : selling/buying equipment, in character only.

Besides those two local channels, there are also intermud channels available,
see 'help intermud' for more information on that.