Sound in Films

Sound within film refers to everything we can hear. From the speech, to the sound effect used. Sound can be used to change the mood of a scene, tell us about the character of the story (villain, hero etc.), provide us with information about the location, and advance the plot.
   There are two types of sound in film:
   Diagetic Sound
Every sound which is coming from sources inside of the world on the screen, including dialogue, slamming doors, footsteps etc.
   Non-Diagetic Sound
Audio elements that we add in/don't come from the fictional world we can see on the screen, including the music and sound effects like the screeches from the film Psycho's shower scene.

Narration is also non-diagetic sound in most cases, with someone talking over the top of differenct scenes. This is used in the opening of The Breakfast Club where we're given background knowledge that the teens have done something wrong so they're in detention. It also gives us the impression that something is going to change the way they view each other.
    Narration can be used to give us just enough information without completely giving it away, which is why it works so well in The Breakfast Club.

Breaking the 4th wall is also used in films. Like in Ferris Buellers Day Off, it's kind of used to "speak sense" into the audience, and in this case, to tell them not to let life pass by so quickly.