The human voice box is a strange and amazing thing. In this video of a quartet singing, you can see the voice box in action via laryngoscope — a tiny camera on a flexible tube inserted through the nose and down the throat.
First, you see the camera enter the nostril and continue over the back of the tongue until you see the larynx. The opening in the center is the entrance to the airway. The whitish bands on either side of the opening are the vocal cords. When they are open, that means the singer is taking a breath. When they are closed, the air is being pushed through them, making them vibrate and create sound. Muscles around the cords adjust the tension on them so they lengthen (making them vibrate faster and produce a higher tone) or shorten (making them vibrate slower and produce a lower tone).
The large flap of cartilage in front of the larynx is the epiglottis. It closes over the larynx when we swallow, so food is shunted back to the esophagus and away from the airway. The process is not failsafe — the human larynx is positioned much lower than it is in other animals, making us vulnerable to choking. But that lower position allows for speech and song, which are enough of an evolutionary advantage to make the risk worth it. We have learned to manipulate this complex machinery to make something not only useful, but beautiful. We pay for it with our own fragility.