In this diagram, the computer is sampling and storing the audio by drawing vertical bars to represent the sound wave and recording the height of each bar:
For a CD, the bars can be 16 bits (2 bytes) high. A bar is drawn 44,000 times a second, and it's done twice (once for the left channel, and once for the right). So:
2 bytes x 44,000 KHz x 2 = 176,000 bytes per second
x 60 = 10.5 MB per minute, or
about 780 MB for a 74-minute CD.