Answer:
You can't literally. You can't really explain what anything literally looks like to a blind person. They have no seeable conception of up and down, left and right, white and black, road and side-walk, long and short, etc.
Notice how I said literally. They can still hear and feel and smell. For the example of a road. You can make them feel water, and smell it, and even taste it. You can tell them from those what water is. You can also make them feel the concrete powder and the texture, make them smell it, and I recommend not making them taste it. You tell them you mix rocks, water, and concrete powder together to get a road. You make them feel the road, listen to what happens on the road, and guide them the length of the road. This will show them a rough seeable idea of the road.
The same thing can be said for color. Give the color a smell, something to feel, or even a taste, and describe it from that to them.
Another difficult way of doing it is telling them that they see nothing. They see the color black, and tell them to go lighter from this point of darkness to describe color becoming lighter.
( it is just a matter of concept ) for a blind man to describe and recognize and store some info in his memory, he would use his other senses like touch, taste, smelling and hearing