Explain the steps of the life cycle of a star. beginning with a nebula and ending with old age/death of a star, explain each step in a star’s life cycle

Gas Clouds (of Hydrogen), starts contracting under the influence of gravitational pull of gas.

As it's contracting, it's pressure & temperature increases, it is called "Protostar" now.

When Temperature become sufficiently high (4 million C), Nuclear fusion starts, & large amount of energy releases.

Energy Travels to star's surface and is radiated in the form of light, heat & EM Radiation.

The contraction of star stops only when "Inward Gravitational pull" is balanced by "Outward Radiant Energy". At this time, star becomes stable in size & temperature.

Contraction continues, 'causes star's outer region to 'boil' & 'expand'. At this stage, it becomes brightest, red giant.

As fuel burns, helium nuclei fuses & form Carbon nuclei further to silicon & further to Iron Nuclei by progressive Nuclear Fusions. At all this stages, star was very unstable.

Star end it's life in many different way & it depends on it's mass, whether it ends as "White Dwarf", "Neutron Star" or "Supernova"

This was a short note on life story of star. Hope this helps!

The inference is supported by evidence in the graph is this is an exothermic reaction where the total release of energy equals a + c.