A movie director is a person who leads the making of a movie (or film). They take care of the artistic things in the movie. They give instructions to the actors and direct the people that work on the movie.
Directors give many of their responsibilities to other members of their movie-making team (called a movie crew). For example, the person who is responsible for the lighting is told by the director what style of lighting he wants and he then creates the lighting for him. It is common for movie directors to work closely with a movie producer. Movie producers are people who control the non-artistic side of movie making. For example, they control all the money that is used for making the movie.
The amount of control a director has in creating their movie is different for each director. It is most common for directors to have some control, while the rest of the movie-making is controlled by the movie studio, and by the people who pay for making the movie. This was very common for American movies made in the 1930s to 1950s. There are a small number of directors who are given complete control over making their movies. For example, Stanley Kubrick, Jean-Luc Godard, Steven Spielberg and James Cameron all had a great amount of control in making their movie.