Stellar Evolution is basically the evolution process of a star. In short it is the process of a Star's changes over time. Stellar Evolution happens over a time frame of millions of years and cannot be easily tracked. There are 3 stages in this process. The first is Protostar. This is the first stage and usually lasts millions of years. During it half of the gravitational potential energy from the collapsing protostar goes into the forming star raising the temperature high enough for thermo reactions to take place. The second stage is Mature Stars. During this stage, the formed star settles to convert its hydrogen supply into helium. As its converted into helium its chemical composition changes to inhomogeneous . The last stage is Old Stars. During this stage, the helium tension is building up causing the core to contract and release gravitational energy. This causes the core to heat up. Eventually the stars core temperature will reach 100million degrees causing helium burning. The outcome of Stellar evolutions depends on the remaining mass of the Old Star.