Tell me more about this "MUD" thing ...

Here's how the typical mud opening screen might look:

Welcome to:
                     --"Ark of the Covenant" Beta 2.6l -

                      Based on ROM Version 2.4b4a Beta
           Original DikuMUD by Hans Staerfeldt, Katja Nyboe,
.========. Tom Madsen, Michael Seifert, and Sebastian Hammer. .========.
//  ,".`'  \       Based on MERC 2.1 code by Hatchet,         //  '.`".  \
||         |                Furey, and Kahn                   ||         |
|| I .'..' |        Quest Code (c) 1996 Ryan Addams           || VI.'.,".|
|| II .'..'|     Quest Code (c)  re-written by Intense        || VII..'..|
|| III`.'."|   ROM 2.4 copyright (c) 1993-1996 Russ Taylor    || VIII,'.'|
|| IV ,','.|      AotC MUD (c) 1998-2006 AotC Ministries.     || IX.'".'.|
|| V '..'.'|   AotC is a creative co-operative ministry of    || X .'..',|
.\_________/             Intense, Kal, and Nyxll.             .\_________/

By what name do you wish to be known?

(had to do a little html edit and use preformating tags so that would look right...)

This is the screen that you would sign in on from AotC. The two drawings of the tablets of the 10 Commandments is what is called an ascii drawing. The gobbledy-gook in the middle is information on what particular kind of mud AotC is and credits for the people who worked toward making it what it is today, including AotC's founders, Intense, Kal, and Nyxll.

Once you create a character (pretty much like logging in for the first time onto a chat site, except you get to choose things like a weapon and what race you are.

Here's an example of a "room" you would find on AotC:

A Beautiful Sanctuary
  There are no windows inside, but a lamp on a table on the eastern wall
lights the temple. A strong aura of protective power and holiness permeates
the air of this holy place.  The flames from a roaring fire send shadows
flickering over the priest and the golden carvings in the walls.  The quiet
movements of the priest echo around the space, mingling with the low murmur
of his constant prayer.  In the middle of the room there is a donation pit
for the needy, and halfway along the length of the temple is a golden
curtain rail with a rich, purple curtain hanging from each side.  It looks
as if the two curtains were once one, and were ripped apart. At the far end
of the room, there is an altar made of twelve stones.

[Exits: north south west up]

   A pit for donations is in front of the altar.
(Golden Aura) (White Aura) A priest stands here praying for the recovery of Old Zion.

If you type LOOK CURTAIN, you will see a seperate description of what the "curtain" in the room looks like. The screen also shows your directions you can move in the bracketed box labeled "Exits". The priest that you see is what is called a mob, it is a program representing a part of the game that you can interact with. In this case, if you've been running around fighting nasty critters (other mobs), the priest will heal your wounds. Sadly, there are no "HMOs"...so you'll have to pay him for his services.

I could fill pages with what you could do with even just a few flicks of your fingers, but I would much rather just invite you to come join me some time and let you experience it for yourself.