you're listening to energy making a journey. It sets off from somewhere inside from the clock, travels through the air, and arrives some time later in your ears. It's a little bit like waves, they start out from a place where the wind is blowing on the water (the original source of the energy, like the bell or buzzer inside your alarm clock), travel over the ocean surface (that's the medium that allow the waves to travel), and eventually wash up on the beach (similar to sounds entering your ears). There is one crucially important difference between waves bumping over the sea and the sound waves that reach our ears. Sea waves travel as up-and-down vibrations: the water moves up and down (without really moving anywhere) as the energy in the wave travels forward. Waves like this are called transverse waves. That just means the water vibrates at right angles to the direction in which the wave travels. Sound waves work in a completely different way. As a sound wave moves forward, it makes the air bunch together in some places and spread out in others.
