Stellar Nucleosynthesis happens when the abundance of star constituent element undergo stellar evolution through nuclear fusion and the modification of one element into another. Its process is created inside the cores of the stars by mixing nuclei of protons and neutrons. The reason of our existence and of the planets is the stars, itself. The continuation of stars burning up enables formation of other elements. Eventually, elements within the stars will continue to flame into the star until it had reached the end of its lifespan. It will later explode into the universe that generates gaseous cloud and produce other heavier metals.
Stellar Nucleosynthesis go through different fusion from Hydrogen phase. Hydrogen phase can be achieved into three processes; (a) Deuterium nucleus is the stable isotope of Hydrogen which is produced from protons into Helium-3. Then two of this atom will fuse and Alpha particles or heavier elements will be created. (b) The Proton-Proton Chain Reaction starts from two hydrogen into forming deuterium with the emission of electrons. I will continue to capture combine until Helium-4 is achieved and (c) Carbon-Nitrogen-Oxygen Cycle.
After the Hydrogen phase, Helium-4 will undertake the Triple-Alpha process which occurs in the stars that have exhausted their fuel of hydrogen. Two of Helium-4 will collide into Beryllium-3. As another Helium-4 crash into Beryllium-3, Carbon will be formed. In here, low mass stars will keep on combining with Helium and heavy elements until oxygen stars starts to drive out outer layer to create planetary nebula while a core of oxygen and carbon remains a white dwarf.
Stars become supernova when mixtures of heavier elements beside Iron are not accompanied by the release of heat because the stars will eventually lose from the gravity pull.