Lighter Weights + More Reps, Heavier Weights + Less Reps

i know from reading around here that lighter weights and more reps dont give you toned muscles although theres still alot of belief that it does. my friend just said it the other day. so what does it do exactly? trains endurance?

though i know that heavier weights less reps trains your strength? well less = maybe about 5? so correct me if im wrong, i do want to teach this to my friend too to prevent him from believing that kinda crap again.