Since all stars begin their lives with the same basic composition what characteristics most determines how they will differ

Mass they are formed with

Explanation:

All stars are born with the same composition such as one quarter of helium, three quarter of hydrogen, and heavier element does not found more than two except their mass. Mass that differ all stars from other stars they born with. How much the mass of a star is large , the star would be as messy.

For example our sun is a star and have large mass four times greater than other living stars. It is found that smallest mass is around 1/12th of sun mass. The masses of a star is determined by its orbit binary. Sun is called a brown dwarf.