Singing from the diaphragm.............?

How do you properly sing from your diaphragm to where it is easy and not uncomfortable....I am like flexing my abs while my stomach is pushed out and it hurts and is uncomfortable while singing........ How do I sing properly or correctly while singing from the diaphragm, and be a great sounding singer like Bruno Mars, Conor Maynard, Andrew Garcia.......ETC...??? HOW???? PLEASE HELP ME>..........