The CRO has a device called a cathode ray oscilloscope which converts the sound waves into electrical impulses which are displayed on a screen. I hope that answers your question :-P
Sound waves are produced by vibrating matter (water, air,etc). Sound is detected by by those vibrations coming into contact with a membrane such as an eardrum.
Sound waves are more precisely described as pressure waves, caused by an oscillating wave of pressure usually in air. Just like dropping a stone in a pond, the waves move out from the source,...