This article attempts to explain how MUCKs work to someone that only has experience with chat-based roleplay.
On IRC and other chat mediums, channels are an abstract thing that may or may not represent a given place. Locations, objects and characters exist because the users in those channels treat them to exist. The world is not a part of the medium at all (which only transmits text) and it is only held together by the users.
This is the main way a MUCK is different. On a MUCK, characters, locations and objects are all formal concepts that have a concrete existence on the MUCK, and the world is actually part of the medium rather than being built on top of it. You're a character that's present in a defined world (with rooms geographically linked to each other, and "exits" to move between them) that continues to exist whether people are there or not. Your character can only be in one place at a time, therefore you are only in one place at a time as well.
Because you're only in one place, you only have one tab/window to interact with. Messages typed in the tab/window will be sent directly to the server as commands, and they do not start with a slash. If you have played any text adventure games, this setup will probably be very familiar to you.
Finding an active room
If a list of rooms doesn't appear already upon connecting, use wa, and see if there's any with any people in it. This is equivalent to the /list IRC command. You will have to actually travel to that location, and there will usually be a list of directions in the form of a series of commands you should enter. If not, there will be coordinates (such as N0 E0) and you can travel to that location with luge latitude longitude, a command that sends you to a given latitude and longitude immediately.
Talking to the other users
To send a message to the room, prefix a line with " (as in "Hello!), or ooc (ooc Hello!) for an out of character message. /me actions exist here too, but on a MUCK the name for that sort of message is a "pose" and the more official command for it is :. /me may not work on all clients.
Because characters and objects are formal concepts on MUCKs, the MUCK stores a description of each which you may look at with look Name, though note that if you look at a person they will be notified.
There are two major forms of private messages. There's whispering (wh Name=Text to send), which only works within the same room, and paging (p Name=Text, similar to whispers) which works across the whole server. Pages, whispers, and OOC messages can contain a pose, too, as in ooc :message or wh Name=:message.
If you want to send a message to someone and they're not online, you can use p #mail Name=Text and they will see a mail notification the next time they're online (similar to how MemoServ works, or how notes work on some sites). If you attempt to page someone who is not online the MUCK will remind you of this command.
Getting your own character
Character creation is something that has to be manually done by a "wizard". Wizards in this context are administrators. To get your own character, use the form here (which sends Austin an email), but you can often get a faster response by messaging a wizard if there are any currently online. You can use wizzes to see which wizards are available, and you can send them a page politely asking them to set up a character for you.
Other notes
Unlike on IRC, there is a timer that disconnects users that have been idle for too long, so connect only when you're going to be around. When someone disconnects due to being inactive, their character falls "asleep", and remain in the room until they are removed by a "sweep", which removes all of the sleeping characters from the room at once. If you reconnect before your character is sweeped away, you will wake up and resume from the same room.
There are a series of bulletin boards that users can post to, namely +read for the main board, cread for the commands/tutorials board, and rpread for roleplay events. To view the boards, type one of those three things as a command.
"Name1 verbs Name2, afar!" seem to be action messages that cross room boundaries, and display a message in both rooms.
"Name verbs you!" always refers to you, specifically, not someone using "you" ambiguously, even though it looks like a regular action. Unlike IRC, messages can display something different to you and to everyone else.
All of the "Name=Text" commands (whispers, pages, mumbles, mail, etc.) allow multiple recipients to be specified. p Name1 Name2 Name3=Text will send a page to all three users.
The server does not support Unicode. Non-ASCII characters will most likely not be sent correctly.
There is functionality for controlling additional in-world characters from one account without making characters for each character. For information, see Zombie.
Misc useful commands
ws: Display a list of the users in the room, and their species and other information. There's also who but that shows less information and does not show all characters.
lookat [container]'s [object]: Examine an object inside another object, such as in a player's inventory.
fa: List all the users connected to the MUCK (excluding people who have opted out of this listing)
@image: Get a list of things that have an image URL associated with them. @image user will show you that users' image, and @image me=http://example.com will set your own image link.
events: Short list of all the events that are coming up, does not give detailed information.
eventlist: More verbose interactive event list that allows you to view information about each event.
last Name: Display when a person was last online.
tb Text: Display a thought bubble with some text. Alternatively, ponder Text