The intensity of a sound is the amount of energy it has. You hear intensity as loudness. Remember the amplitude, or height of a sound wave is a measure of the amount of energy in the wave. Pitch and loudness are two ways that sounds are different. Another way is in quality.
Some sounds are pleasant and some are a noise.
Compare the two waves on the right. A pleasant sound has a regular wave pattern. The pattern is repeated over and over. But the waves of noise are irregular. They do not have a repeated pattern.