Stages of a Star Main Sequence

Main sequence is the longest stage of a star. This stage is largely what people think of when they picture a star. During the main sequence, stars send out tremendous amounts of energy and heat. It is that same energy and heat that makes life possible on Earth. Over time, the nuclear fusion in the star causes the star to shrink.

The length of time a star spends in main sequence depends on its mass. The larger the star, the shorter the lifespan. The reason is that it takes large stars need more matter to keep the star at equilibrium. As a result, the star burns through its supply of hydrogen and helium over a shorter period of time.

Source
http://aspire.cosmic-ray.org/labs/star_life/starlife_sequence.html (fair use)