How is a star formed?

Believe it or not a star is formed out of a cloud made of cool, dense molecular gases. In order for the star to become potential the cloud has to collapse and increase in density.

There are two different, common  ways that the cloud collapsing (to become a potential star) can happen. The cloud can either collide with another cool, dense molecular cloud to create a collision and then the cloud would collapse. Or it can be near enough to encounter the pressure caused by a gaint supernova. Several non-potential stars can be born/created at once with the collision of two galaxies. In both ways of making the stars become potential, heat is needed for the reaction. This heat comes from the mutual gravity pulling all material inward.

The life cycle of a star is dependent upon how quickly it consumes hydrogen. For example, small red dwarf stars can last hundreds of billions of years, while large supergiants can consume most of their hydrogen in only a short few million years. Once the star has consumed most of its hydrogen, it has reached its mature state. This is how a star forms.