The producer is the manager of the film, and deals with the money and schedules.
The director is the creative manager of the film; the director calls 'Action!' and 'Cut!'.
The cinematographer/director of photography is responsible for the look of the film - the photography.
The screenwriter writes the script or screenplay.
The leading actors/the main actors are often famous stars, and they have the most important roles in the script.
The supporting actors are the other actors in the film, they have less important roles in the script.
The extras are people in the background of the film, they usually don't speak in the film.