Sound is caused by coliding matter resulting in matter vibrating, creating a sequence of pressure wave that propagates through other matter.
Sound can ony be heard if it is composed of frequencies within the range of one's hearing and of a level sufficiently strong to be heard. For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz), although these limits are not definite. The upper limit generally decreases with age. Other species have a different range of hearing. For example, dogs can perceive vibrations higher than 20 kHz, but are deaf to anything below 40 Hz.
For an example try hitting a empty glass with a steel spoon. Both glass and spoon will vibrate creating sound, but we can only hear the glass vibrate, because the spoon's vibration is outside our range of hearing.