Answer:
Stellar nucleosynthesis is the process by which stars operate. Stars are massive nuclear fusion engines, and they consume hydrogen, the most abundant element in the universe, and fuse it into helium. They do this throughout most of their lives, and then fuse helium and heavier nuclei to make heavier elements up through iron later in their lives. Stellar nucleosynthesis is the basic "life story" of stars. But what about those elements heavier than iron?
All the trans-iron elements are formed in a supernova event because those heavier-than-iron elements do not liberate energy when being fused. It takes energy to make them happen, unlike the fusion processes that create elements up through iron. The endothermic fusion reactions that create the heavier elements are only possible when the star collapses after exhausting its fuel, and the collapse compresses and heats the material and provides enough energy for the fusion of the heavy elements. A big explosion follows, as you know. And only stars moderately large (a bit bigger than our sun) have sufficient mass to go supernova and create these heavy elements. You'll find links below for more information.
Star fusion is where a star heats up to cause the atoms the smash into each other creating a new mineral which with have a smaller mass that the first. the excess mass is just PURE ENERGY.