Scientifically speaking, sounds are vibrations that spread as an audible mechanical wave through a medium of air or water. The hearing organs are then stimulated by the vibrations.
Sound, which is the movement of air, travels in waves. All sounds can be reduced to, or created from, a singular wave. When listening to sounds, parts of the human ear are vibrating. When speaking, a voice causes the air around it to travel, which causes pieces of the ear to vibrate accordingly.
Microphones operate in a similar way. After sound is emitted through the diaphragm, it begins to vibrate and is converted into a signal. On the other hand, when someone receives a signal, it causes pieces of the speaker to fluctuate back and forth, which then causes the air around it to travel. This is to ensure that sound is listened to as efficiently as possible.
In many ways, sound is very much like light. They both emerge from a sure source. However, while light can travel through a vacuum, sound cannot do the same. It requires a medium to maneuver through, such as glass, metal, water or air. Sound waves tend to lose kinetic energy as they travel, which explains why a person cannot hear things as well when they are originate from a distance.