You can also get lost or confused if you jump right in, so be sure to read this document before starting. TinyMUD is one kind of MUD program. The LP- family of MUDs are based on roleplaying adventure games. In these, your character runs around killing monsters, finding money, and making experience in the quest to become a wizard. There are still other programs, called MUCKs or MUSHes, that extend the TinyMUD programs by including a usable programming language.
MOOs have an object-oriented programming language, and are more 'social' in nature.
UnterMUDs can connect to each other directly, and have both a scripting language and a programming language. We suggest that you experiment around to see what you find is the most interesting. If there's one thing MUDdom has, it's variety. Every Friday a quite complete listing of MUDs is posted. MUDs are run on many fine computers across the world.