Your first step in really understanding how sound works will be to aquire a knowledge background in the area of waves.  Sound is a type of mechanical wave and has many properties similiar to all types of waves.  The best way to start is to dive in and begin to surf!  Ha Ha!  Start by reading and working through the tutorials Lesson 1: The Nature of a Wave and Lesson 2: Properties of a Wave at this website.

After reading and engaging in the Wave tutorial you should go to the Wave Review Activity and complete it.