It takes very precise equipment to read the data on a CD. When you play a CD, the CD player converts the stream of numbers back to an analog wave using a digital-to-analog converter (DAC).
A laser beam in the CD player scans the surface of the CD, from the center outward and is seen through a tracking lens. The pits and the flat surfaces, called lands, reflect the beam of light differently. The data is received by a photoelectric cell in the form of a series of light pulses corresponding to the bumps and lands on the disc.
