On a movie set, the director is the person who is in charge of the creative impulse. He makes sure the actors act as they should; he decides of the frame and of the position of the camera. In short, he decides what ends up as the moving pictures in the final movie. His job might also include that of the editor, director of photography, and (less often) that of co-writer.
The director is also in charge of the financial aspect of movie; primarily the budget. He must make sure the movie is made within the budget and on schedule.
In short, he is the coordinator of what the movie is to become. In Hollywood, however; it is the producer who has the final say over what happens to the movie. His job is to make business decisions. Whereas, in the rest of the world, motion pictures are still sometimes considered an art, and usually the director has the final cut which means he has much more control over the movie.