There are 3 main components which produce a healthy, well-functioning voice:
Breathing, Phonation and Resonance.
The first stage of voice production is the Breath. The breath is the energy with vibrates the vocal cords and creates a sound wave. The amount of air pressure we apply to the vocal cords is important: We need to constantly maintain a balance between the muscular energy involved in cord closure and the pressure of the breath. Too little breath will not create a strong enough sound wave and too much air will blow the cords apart and produce a breathy sound or make the cords over tense and unable to move correctly.
The larynx comprises of a supporting structure, made of cartilage, to which the complex muscles of the vocal cords are attached. It is located at the top of the trachea (wind pipe). The vocal cords open wide during normal breathing, close tightly when swallowing food and vibrate against each other when brought lightly together during exhalation. During singing the vocal cords are capable of producing a wide range of pitches. This is achieved by varying the length, thickness and speed of vibration.
Resonance is the physical phenomenon which occurs when sound waves enter or pass through a cavity. Example of resonators are organ pipes and acoustic guitar and violin bodies. A resonator of a given size is tuned in to a spacific note, hence the array of pipes in an organ and the single note capacity of a digeridoo. The voice is resonated in the vocal tract, the space in the throat above the larynx and the back of the mouth. The body also has sympathetic resonators which repsond to the initial resonance, these are felt in the chest, face (behind the nasal cavity) and in the head.