Tells are a way to communicate with players who are not in the room with you or to communicate relatively privately with players who are. To speak to someone in this manner, the syntax is: TELL <player> <whatever>.

For instance: 

tell roark Why don't Dwarven women shave more often? They really could use it.

(This, of course, may not elicit quite the friendly response you are looking for from Roark, but it will amuse this writer, at least.)

You may abbreviate tells by simply typing all or part of the player's name, followed by what you wish to tell them.

For instance: 

phae Why don't dwarven women shave more often? They really could use it.

Note: You can modify this behaviour with CONFIG NAMETELLS [ON/OFF].

If you wish to simply reply to the last person to speak to you, then all you have to do is type REPLY <your message>.

If you do not wish to listen to tells at all, type TELLSOFF. To begin paying attention to tells again, type TELLSON. When you login, your tells will automatically be turned on.

You can see a history of the last tells to you during your current session by typing TELLS. If the tell as listed is abbreviated due to length, you can type SHOWTELL <tell #> to see the full text.

Most other forms of telepathic communication, such as CT (for cities and communes), GT (for guilds), CLT (for clans), and others can be used with a *TELLS syntax to get a list of the 20 most recent things said. Examples: CTELLS, GTELLS, CLTELLS, OTELLS, OTOTELLS, OTITELLS, OTCTELLS. 

You can also SHOW*TELL <num> to view a specific tell, for example SHOWCTELL 5, SHOWGTELL 10, SHOWOTELL 10, or *TELLS FULL to see all of the history in full - e.g. CLTELLS FULL.