How do I breathe from my diaphragm when singing?
You cannot feel or steer the diaphragm directly. It is the muscle under your lungs, it contracts when you breathe in, and it relaxes as you breathe out. What singers mean by "breathing from the diaphragm" is two things: breathing in low, so your belly and lower ribs expand instead of your shoulders lifting, and then letting the air out slowly and steadily, using the muscles around your waist and ribs. A long, even hiss on one breath is the simplest way to practise the second part.