The details which led to our understanding of the evolution of stars occurred shortly after the first decade of this century. Stars, just like people, really aren t all that different. In the human experience people may look radically different, but they all function basically the same way. Their lifestyles, however, are very often influenced by their physical characteristics, such as weight. That s what Hertzsprung and Russell found for the stars.
All stars belong to the same family too.
They are changing hydrogen into helium via nuclear fusion. It s a nuclear reaction, not a chemical one. The intensity of the reaction is a function of the temperature and pressures generated inside of a star. And that is a factor of a star s mass or the quantity of material which it contains. A rough idea of what is happening inside of a star is revealed by that star s color.