Sound is created by vibrations in the air. For example, if you hit a drum, you see the drum skin move. As a result, small changes in the air pressure are created, so that the air starts to vibrate. Sound spreads in sound waves, just like water spreads in water waves. And just like water, sound can reverberate against a wall or bend around a tree.
Sound can also be propelled through water by small variations in the water pressure. The human ear is not suited to this, but a whale has excellent underwater hearing . Did you know that sound carries further under water than it does above water?
Listen to the sound of a whale here: