Darkness is the absence of light. In order to see our eyes must receive light. We are able to see because light reflects on objects and the reflected light becomes a mirror image in our eyes.
Want to learn more? Watch the video:
https://www.youtube.com/watch?v=LY38mXrJmuw
and then play a game on:
http://www.bbc.co.uk/schools/scienceclips/ages/5_6/light_dark.shtml