Players can communicate to other players using the 3D mud client using the communication panel at the bottom of the 3D client. For example:

Like all muds players can talk to players in the room (say), shout to everyone in the game (shout) or tell a particular player something.
The commands sent to the mud can be changed in the mudstrings element of the config file. For example instead if you want to 'say' using the ' instead of the word "say" you could use:
say="'"
Likewise for shout and tell.
It is also possible to set the default form of communication using the mudstrings attribute 'initchattype'. If initchattype="shout" for example then by default when a player starts the mud client everything they say will be shouted. This can be useful if your game has a low volume of players.