I am trying to understand what sound is.
All sounds are waves produced by the vibrations of material objects.
The human voice results from the vibration of the vocal chords. In each of these cases a vibrating source send a disturbance through the surrounding air molecules in the form of longitudinal waves. The frequency of the sound wave is identical to the frequency of the vibrating source. Let us pause to reflect on the physics of sound while we are listening to our radio. The radio loudspeaker is a paper cone that vibrates in rhythm with an electrical signal.