When a dog barks or a guitar is strummed, it makes the air vibrate, and these vibrations carry the sound to your ears. The vibrations that carry sound through the air are called sound waves. Sound waves are not like waves in the sea, which ripple across the surface in lines.
Sound waves travel by alternately squeezing and stretching the air.
When a sound is made molecules in the air nearby are squeezed together. These molecules in turn squeeze those next to them, and then are pulled back in place by the molecules behind them. Sound waves actually travel faster through solids and liquids than through air, because the molecules are more closely packed. In a vacuum there is complete silence because there are no molecules to carry the sound. The boom of thunder sounds very different from the squeal of a car braking.