Germ powder is not made of germs. It is used to simulate germs to test cleaning habits. Since it fluoresces under ultraviolet light, you can see how much is left behind after cleaning.
Sprinkle a small amount in the palm of you hand or on a surface to be cleaned. Wash as you normally would. Test with ultraviolet light to illuminate any powder that remains. This is where germs would have survived the cleaning.
Germ powder is a non-toxic product.