A CD drive has a laser at one end and a lens at the other. The laser is used to read the data from the top of the disc, while the lens focuses light onto it so that it can be properly read by a sensor inside the unit.
The CD player’s job is to read data off of a disc and translate it into sound. It does this by focusing a laser onto the spinning disc or DVD to produce an image on its surface whose height varies according to which frequency the corresponding sound should have. Sensors detect irregularities in this height so they can create corresponding frequencies, even if you place your hand on top of it while listening to find out what else I know. We all know that CDs are encoded with information related to digital representations of analog audio signals, but the reason that discs are flat is actually that early computers were too slow at reading from rotating platters which led engineers to return back.
