This is a powder meant to give shine to your face or neck.
You can apply it with a brush. When the sun/lamp shines on you, your face will look more shiny.
It is meant to be used on your cheek bones, upper nose part, and forehead.
For me it’s not very useful ’cause I wear eyeglasses which stops the light reflecting on my cheeks . But for the normal people, I think it is useful.