For newcomers to the MU roleplaying format, but for anyone that has roleplayed online in different formats such as forum roleplay, virtual tabletops, chat rooms, or freeform roleplaying in MMOs, they might find MUs a little bit different and tricky at first, but most find the MU format extremely rewarding once they get a little used to it and the gazillion commands used from a throwback command line. Trust me it's worth it.
MUs are designed to facilitate both the large, epic overreaching stories that changes the entire game world and pulls every character into it with the potential to be a core protagonist, as well as the small, intimate stories of personal character development that give the larger stories meaning, and allow all the stories to interact together and develop organically. One character might be a princess trying to help her dishonored house rise back to glory, another might be a criminal with dark allies he can't quite control, another might be a scholar finding out uncomfortable truths, or any of a hundred stories that all overlap in the same shared world and change and influence each others' own stories. MUs attempt to have the storytelling benefits of more freeform environments (like MMOs, forums, chatrooms) while having the organizational advantages of formats like tabletop for easy conflict resolution and keeping stories in order.
MUs are pure text-based formats that can feel a little bit similar to a pure text based MMO, even if every system we have is based around supporting roleplay, and trying to foster the best stories we can make. A player connects to the game by clicking the 'Play Online' button on the webpage here: http://play.arxmush.org/webclient or by downloading and using another client such as Potato http://www.potatomushclient.com or Atlantis http://www.riverdark.net/atlantis for macs. From there, someone can create a character, or apply to play an existing character from the roster of available characters. For details on character creation or choosing a roster character, see the help file on Getting A Character (under 'help Getting A Character' at the command prompt) or by clicking http://play.arxmush.org/topics/Getting%20A%20Character/
Once someone has a character and logs into the game using one (with 'connect <character name> <password> at the login screen), they will have access to all the commands that allow for In Character actions and communication, as well as Out of Character communication, with the commands being separate to eliminate the ambiguity between characters speaking to one another and players speaking to one another. For a list of guides to the different systems, please see the Arx Systems Guide ('help arx systems guide') and for a run down on IC and OOC communication, please see the Communication Guide ('help communication guide').
While on a character and In-Character mode, they find themselves in the city of Arx, and every room they move into can contain other characters and events that allows for localized IC interactions. By moving around the map of rooms called the grid, players can easily have their characters happen upon ongoing RP scenes organically, arrange small scale or large scale RP scenes as they like, and exert a degree of control over the different stories as they choose their level of involvement using IC and OOC tools. There could be dozens of different public or private RP scenes going on at any one time, but a character can choose which ones to involve themselves in, and which stories to pursue, even though many of the stories will be having ripple effects on other ones.
The biggest advantages of a MU* Roleplaying format compared to freeform sandboxes like an MMO, forums, chats and similar formats is the relative ease that players and staff have to initiate and guide new stories, and to overlap them in organic ways to create more RP unexpectedly. In other formats, players roleplay stories with their friends and it doesn't affect the setting outside of their sandbox. On Arx, that's not the case at all, and any character's actions can have effect characters they've never met and might not be aware exists, and players will likely have no idea what way the different stories will finally end up, or how they will all overlap in the context of the giant metaplot that unites the game. It's a lot of fun, and we all hope newcomers to the MU format enjoy it. Don't be afraid to talk to staff if you have any questions at all.