This is a picture of the bells in the bell tower at UC Berkley. I visited Berkley with my family over the summer and we went up the bell tower, there was an awesome view and the bells were really cool too.

Each bell in this elaborate contraption has its own pitch and when played together music is made. When the thing inside the bell is pulled by the strings connecting to it, it hits the side of the bell, producing a vibration. The whole bell vibrates and those vibrations go off into the air, making noise!

The faster the thing hits the side of the bell, the higher the frequency of vibrations. As frequency increases, wavelength decreases. Wave speed is dependent upon the medium the sound wave are traveling through. 

When two waves meet their interaction is called the principle of superposition. The waves pass through each other, but as they meet, the briefly combine. If the crests of the waves match, the add to each other and form a super crest, same with the troughs, but if the crests are opposite then the crest of one wave the the trough of the other subtract from each other and if the waves are identical but 180 degrees out of phase then the waves will cancel each other and you will not be able to see the wave in its medium.