Sound, what is sound?
Sound is an important element in videos and films. Although usually, "good sound" are not meant to draw attention to the sound, and negate the visual -- because that'd be radio, not video, but rather enhances the overall experience of the video / film -- the combination of visual and audio simulation.
We can divide the many different kinds of sounds that can be found within a video / film:
1. Voice-over narration
-- Voice over narration is usually recorded after the filming of the scene(s). They are usually added sound tracks that are recorded in post production rather than on-camera during production.
2. Foley (and sound effects)
-- This category basically includes all sound effects, whether created by a Foley artist or prerecorded, that are added during post production.
3. Music
-- Music can and is an important element in video and film. Usually added in at post production, music that are selected or recorded correctly can help enhance the mood of the scene greatly and bring the film to life.
4. Dialogue
-- The most common element of sound in all films. Since most dialogue recording will be done on-camera during production, it is essential to know the specific microphone selections and microphone placement that is suitable for each scene.