How does a tuning fork make a sound?

 Sound waves are produced by vibrating objects. Whether it be the sound of a person's voice, the sound of a piano, the source of the sound is always a vibrating object.

A tuning fork is a good example of how a vibrating object can produce sound. The fork consists of a handle and two prongs. When the tuning fork is hit with a rubber hammer, the prongs begin to vibrate. The back and forth vibration of the prongs produces disturbances of surrounding air molecules. These regions are transported through the surrounding air, carrying the sound signal from one location to another. The tuning fork's vibrations interact with the surrounding air to create sound.

In solids, sound can exist as either a longitudinal or a transverse wave. But in mediums which are fluid (e.g., gases and liquids), sound waves can only be longitudinal. 

A tuning fork is a two-pronged metal fork that can be used as an acoustic resonator. Traditionally, this tool has been used to tune musical instruments. Tuning forks work by releasing a perfect wave pattern to match a musician's instrument.