This document discusses the use of sound in films. It explains that sound is carefully crafted in post-production to emphasize important sounds and set the proper atmosphere. Sound can be diegetic, meaning it exists within the world of the film, or non-diegetic and comes from outside the film. Examples of each type are provided. The document also discusses other sound design elements like synchronous and asynchronous sound, and how sound is used to guide the audience's understanding.