Stellar nucleosynthesis is the process through which stars create elements within their cores, excluding hydrogen, formed after the Big Bang. Stars’ cores, with extreme pressures and temperatures, facilitate nuclear fusion. In the p-p process, hydrogen nuclei fuse to form helium. More massive stars follow the CNO cycle, combining carbon, nitrogen, and oxygen nuclei to create elements beyond helium. As stars deplete their fusion material, core contraction increases temperatures, restarting fusion until iron is formed. Iron marks the threshold where fusion consumes more energy than it releases.