Pulse Width Modulation, is a DAC (Digital Analog Convertor) using only numerical components (outputting only 0v or 5v values)<br />
Using an entry clock, you output several signals 0v or 5v in order to result an average fix value between 0v and 5v, for sample 2.3v. Changing like it the speed of a small electric motor (speeding it up or slowing it down) as you want but using at input only two values : 0v or 5v.<br />
Using a quicker clock, you can generate analog signal, like sound music.