When we look at a lighted candle, the light from the candle travels into our eyes and enable us to see the candle. Lighted candle is an example of a luminous object.
At the same time, this light spread out in all directions, falls onto the surface of objects, bounces off and is reflected into our eyes.
Non-luminous object does not emit light, it reflects light. In this way, we are able to see the object. In a totally dark room, there is no light source. Hence, no light falls onto the objects in the room and no light is reflected into our eyes. As a result, we cannot see anything in the room.
When you look at a mirror, light that falls on you bounces off onto the mirror. The mirror changes the direction of light by reflecting it back into your eyes and you see your image in the mirror. The image formed by mirror is a virtual, upright and laterally inverted.