Prowess is a triggered ability that gives the creature that has it +1/+1 until end of turn whenever you cast a noncreature spell. Any spell you cast that isn't a creature will cause prowess to trigger. Remember that lands aren't spells, so playing a land won't cause prowess to trigger. Casting a spell that's a creature and also another type (such as an artifact creature) is still casting a creature spell, so prowess won't trigger in that case either.