Stars are made up of dust and gases like hydrogen and helium. Inside the star at it's core hydrogen atoms combine to become helium. It is also known as Nuclear Fussion. This helium is used as the star's fuel. This fuel burns so rapidly and fiercely that we are able to see the star which is very distant away. During this burning process the temperature of star reaches to millions of celsius. And when this fuel or all the helium is used up the looses it's shinning power and proceeds to it's other stages of lives such as red giant, supernova, white dwarf....neutron star and finally black hole.