Stars are complex and giant balls of matter that have many things to understand about. Stars are born of gas and dust and have a life cycle based on their original mass. All stars start out in their main sequence, but the first difference between the mass of stars is when they stop producing energy. The low-mass stars become giant, and the high-mass stars become super giant. For low-mass, the star then becomes a planetary nebula, then finally a white dwarf. High-mass stars become a supernova, a giant explosion, then can become either a neutron star or a black hole. While still in the main sequence, though, stars go through nuclear fusion to produce heat and energy. This is a process where hydrogen molecules fuse into helium.
Nuclear Fusion
Nuclear Fusion