A role playing game is very simple to explain. It's a big game of let's pretend. It can be done live, face to face, as in Dungeons & Dragons, or online over the internet, which is the method I prefer, myself. With face to face games, the one in charge, or the game or dungeon master, chooses the world the players will be in, and each player creates a character complete with race, looks, age, personal quirks and life history. The game master then sends them off all together on a wild adventure or quest. Online playing is a bit different in that there are literally thousands of worlds a person can chose from, from Star Trek, to Harry Potter. They are done either text or video based, sometimes with typed descriptions for the various rooms, objects and people that you can see to help you play better. It's a lot like writing a story sometimes, only the player just writes their own character's part while the other players write their own characters' reactions. Once the player chooses a world they like, they create a character based upon that world, once again with looks, age, quirks and history, go on the game and simply pretend to be that person. Some days exciting plots or romance may happen, other days simply ordinary things, at least as ordinary as they get in such fantasy worlds. You never really know what's going to go on, which is part of what makes it so much fun.
Most types of online games have acronyms, and certain types of activities associated with them. There are many types, but here are the most popular and common ones.
These first types of games are usually "hack and slash," meaning the players go around killing monsters and evildoers to win points, gold, and magical objects. It's very much like Dungeons & Dragons, with actually very little emotional role playing involved. The character's stats are very important, as the player wants to have as powerful a character as possible. If you want to relieve stress by going out and killing things on a game instead of doing real damage, then these are for you.
MMORPG - Massively Multi-player Online Role Playing Game
MUD - Multi User Dungeon/Dimension
MUX- Multi User Xperience
The other types of games are more "slice of life" sort of games, with everyday as well as extraordinary things happening. The characters played actually live here. No points, money, or magic objects are given, and there are no winners or losers. The player just portrays their character as best they can. Sometimes it can get very angsty, and like a soap opera, but if you like more emotionally charged role play, then you'll want to choose one of these.
MUSH - Multi User Shared Hallucination.
MOO - MUD Object Oriented
MUSE - Multi User Shared Environment
MUCK - Multi User Chat Kingdom - This type is the sort of game most people will want to avoid. They host what's known as Furry RP, where there are animals, or people, or both, doing sexual and kinky things in role play. Most of these are essentially porno, so research a MUCK VERY carefully before you get on to play.
There is, of course, the difference between the MMORPG, MUD and MUX and the rest of the types of games, due to the differences in the sort of role play the player experiences, but the other, more important difference between each of the types is the programming involved in creating the game, and the commands players can use to do things. When you get on a new type of game, the best thing to do is first look through the help and information files to familiarize yourself with the games.