How is most of a star's total life spent?
Oh, watching Youtube videos and spending too much time on solar Facebook! Just kidding! Burning hydrogen and releasing huge amounts of energy is a stars main past time.
From the time a star lights up, it starts to "burn" its available hydrogen which releases huge amounts of energy in almost the entire range of the electromagnetic spectrum (but for our star, mostly in the visible range). This fusing of hydrogen atoms together converts the hydrogen to helium and in the process releases a lot of energy - the same process that produces the destructive energy of hydrogen bombs. This goes on for maybe around 90% of the stars life.
Toward the end of a stars lifetime, it usually starts to expand into a Red Giant star. At this stage, it has burned most of its hydrogen and starts to "burn" helium to produce the element carbon and later oxygen. The star goes on producing new elements like neon, magnesium, silicon and finally iron. When this process of generating new elements stops, the star either collapses and emits the remaining gases as a nebulae or it explodes as a supernova star.
The elements produced by the dying star drift around the galaxy for eons and often eventually come together again to produce a new star and solar system with planets.
Its true to say that all of the atoms of carbon and oxygen in our bodies today were once part of a star. You are literally made of "star dust"!