Answer:
You squirt a moderately sized puff on your hand and rub your hands together to even the load of mousse on the hands the you apply to hair rubbing it in with your fingertips.
Good answer, but left unfinished. Don't forget that your hair needs to be wet. After working in into your hair, use a finger-style diffuser and a blow dryer on low heat to give your hair some shine, otherwise you'll have tiny white flakes or residue.