Electronics are often times based in the "binary" language, meaning that everything is presented by 0's and 1's. It is the easiest scenario because you only need to find out of something is "on" or "off." CD's are composed of many concentric grooves, much like the old vinyl records. Each groove of a CD is like a long trench. However, the trench is not uniformly deep, but rather there are two different heights. Imagine the bottom of the trench being a race track with a set of irregularly spaced hurdles. Now, a laser shines into the trench, hits the bottom, reflects back out, and then hits a detector that records the event. Depending on if the laser hits the bottom of the trench or hits the top of a hurdle, a different signal is observed by the detector. Since we have only two levels, there are two different output signals. One signal is assigned a value of "0" and the other a value of "1" - this is how binary information is stored on a disc! The binary signal is then decoded by the CD player to be turned into the music that you hear.

As far as CDs go, I don't know that much about them.A laser is used to read digital bits (zeros and ones) which are used as a code that the electronics inside the CD player can convert to sound. Computers use the same basic method. People I talked to in the lab thought that there are (very small) grooves in the CDs that are read >out as ones or zeros depending on how long it takes the laser light to reflect off the CD and return. Sounds good to me.

CDs contain a code of bumps and flat spots. The CD player shines a light on the CD to determine what combinations of bumps and flat spots there are and then translates that code into a wave of electricity. This wave of electricity then moves a piece of paper or plastic back and forth to create a sound wave that we can hear.