Answer:
When you sing from your stomach or rather your diaphragm, the sound is usually stronger and your chest doesn't hurt as much. Usually you do that when singing a long phrase or loudly so you don't run out of breath. When you sing from your throat...actually, I don't think your supposed to sing from your throat unless you're singing quietly; because you sing with your "head voice" to keep the high notes in pitch, and you sing with your diaphragm to have more....control, power,whatever you want to call it.