While you may only be interested in audio, matters of digitization are much easier understood when we look at how the same concept is applied to images. In this excellent presentation by professor Sapiro in his Duke University class, Image and video processing: From Mars to Hollywood with a stop at the hospital, he presents a surprisingly approachable video for a university course. So don't be intimidated by the origins of the lesson and watch the video:
The video is HTML 5 and nicely understandable even at 1.5X speed. I actually watched it at 2.0 which is usually not usable but it almost is here although if you are knew to the topic, I don't recommend it.