Stellar fusion is the process by which stars generate energy by fusing lighter atomic nuclei into heavier ones. In the core of a star, extreme temperatures and pressures allow hydrogen nuclei to combine and form helium. This release of energy creates the light and heat that we observe from stars, including our own Sun. As stars evolve, they can fuse heavier elements, such as carbon and oxygen, depending on their mass. This process continues until they reach iron, which cannot release energy through fusion. Eventually, the star may undergo a supernova, dispersing these elements into space, contributing to the formation of new stars and planets.