You-tube. No, dry shampoo is something that you sprinkle on top of your hair without rinsing it out. It's supposed to absorb fat and odour without you having to wash your hair. I have no idea why anyone would want that, but maybe it's handy when you had your hair done nicely and don't want to ruin it with water.
You-tubes about making your own dry shampoo are also out there.