Sound waves are created by objects vibrating back and forth, which causes the air to vibrate. Your ear hears changes in amplitude as volume, and changes in frequency as pitch.

Slow motion movies of guitar strings, cymbals, and car speakers show how they create sound by vibrating back and forth, pushing the air and creating sound waves.

Resonance is when a wave fits perfectly in an object, causing the wave to get bigger and bigger. Here are examples of resonance waves in a tube. In the speed of sound lab we use a tube with one end opened and the other closed. You can also get resonance in tubes with both ends open or with both ends closed.

Resonance can have pretty drastic effect, like in this bridge. The wind started shaking the bridge at a frequency that resonated in the bridge.

The Doppler effect applies to all waves, but it is most easily experienced with sound, as can be seen with this recording of a car driving past.