Sound is created through the vibration of air. When something produces vibrations, it creates sound waves. The movement of the vibration through the air is what people hear when they hear sound.
Vibrations are the way that sound is made. For example, imagine a drum being hit with a mallet. The drum vibrates, creating a sound wave. The reason the drumhead creates sound waves is because it moves outward and inward, which pushes and moves the air around it. The air gets pushed by the drumhead, so it moves faster than the surrounding air. As the faster-moving air travels, it collides with the air around it and transfers the extra energy. The movement or vibration of the air molecules continues to get transferred farther and farther away until the energy dissipates.
There are many factors that can have a direct effect on vibrations and thus sound. For example, a louder sound is produced when the vibrations are increased in intensity, and a higher-pitched sound is heard when the vibration frequency is increased. In fact, the frequency of the vibrations is what allows an organism to hear. There are many frequencies humans are unable to hear, but other animals, such as dogs, can.