Game Mastering

The Art of Running the Game
Referee, world-builder, record-keeper, the person behind the screen is the unsung hero of the game. Mr. Gygax made it just so, and tells us as much in his Game Masters Guide, for without the GM putting forth effort even before play begins, there is no game. To view the job as merely one of necessity is an injustice, however. Taking one's turn behind the screen can be, and should be, quite rewarding.
Acting as the impartial adjudicator of the rules governing play of the game is the role of the referee. In a role-playing game, as in table-top wargaming with miniature figures, it falls to this individual to set the parameters for play and to describe the scenario. Keeping track of important game information is another task that this person usually assumes. Record keeping is especially important in campaign play where details are carried forward affecting future game sessions.
Fairness and consistency in the interpretation and application of the rules is important and forms the basis of the trust that must exist between the referee and the players. It is the basis of the referee's legitimacy. The responsibility of enforcing the rules makes the referee's word final during the game. To avoid disputes is why the game has a referee.
The game master or dungeon master creates the context for play. Whether that involves drawing a map on grid paper, setting up replica terrain, or merely describing the surroundings and situation in which the players are to imagine their characters, the game master devises the world in which the game's action will take place. In a role-playing context, it also falls to the referee to play the part of all the characters not controlled by the other players.
Keeping record of the passing of time and the achieving of goals is also the responsibility of the referee or game master. Recording hit points, experience and treasure is a part of the game and forms one element of the multi-tasking experience of the game master. If campaign play is the goal, it becomes important to keep records not only of how much time passes but also what non-player characters have interacted with the player characters, and what knowledge of the setting has been revealed to them. Details are what brings the imaginary world alive and consistency across sessions is highly desirable.
This all may seem like a big responsibility and one that is often underappreciated, but it is great fun to watch the game you have set up unfold during play. It is only through the interaction of the players that a world you created really comes to life. And players will surprise you, entertain you and at times frustrate you. Remember, it's all in an effort to have fun together playing a game everyone enjoys.
It is important to note that the referee of a role-playing game is also a player. The referee or game master is there to have fun too. Not by killing or humiliating characters, but by seeing the setting they have worked to create come alive through play and provide entertainment for others. The referee desires for the players to have fun and it should be the case that players also make an effort to see that the referee has fun as well. It's just part of being a good player to do your part to help others have fun too. Think of it as one element of "mastering the game".