Question

how do we hear sound which factor is used

Answer 1

due to the presence of medium we can hear.... due to this reason we can hear on the earth but we can't hear in the space because there is no any medium present

Answer 2

we hear sound by our ear
our outer ear also known as pinna ,collects the vibration (as vibration is the reason of generation of sound )
then that vibration enters middle ear through auditory canal at the end of auditory canal there is ear drum
which get vibrate by the vibration then this vibration enters middle ear where three bones amplify the vibration
bones are - stirrup , hammer , anvil
then amplified sound enters inner ear where sound gets converted into electrical signal
these signals then sent to brain and our brain finally interprets and we hear a sound

hopeit helps you! !☺