All substances can have sound traveling through them. But it doesn't get from one thing to another to well. Alot of the time sound bounces back off the walls or floor. This is an echo. Amplify means to make a sound louder.
Decibels are how loud sound is.
An amplifyer at its simplest is a big cone. You can also use the cone to hear stuff louder by putting it up to your ear. Thunder is 110 decibels. A wave of sound can be changed from electrical energy into sound energy and than back again. It does this so it can be carried over long distances such as the telephone.