Question

why we are not able to see in darkness

Answer 1

We see things when the light from a particular object is received by our eyes. But when there is darkness, no object is reflecting lights. Hence there is no change of receiving light from those objects and therefore we can't see it. That's why it is called "darkness is the absence of light only"

Answer 2

when light enters in our eyes then only we are able to see but in darkness light do not enter our eyes so we are not able to see