Sound can "Sync" with the action in the movie. Selecting the Sync drop down offers four choices:
Event will force that a sound is played from beginning to end when the frame playing it is reached.
Selecting Start will ensure that two instances of a sound file are not playing simultaneously.
Stop will force an instance of Sound file not to play.
Stream will sync the sound file with the animation so that it animation and sound file play in time with each other.
Finally, sound can be looped any number of times. This works well for background sound tracks.