Before I start to explain all stars' life cycles, I have to give credit to Fred Hoyle. From his ideas and theories, I get my explanation of the cycles. So stars need to have a dynamic life cycle.
Stars form when hydrogen atoms in space are pulled together in bigger and bigger spheres.
The reactions on the sun are like atomic bomb going off on Earth. Except the atomic bomb would be like a balloon popping compared to the entire Earth exploding. The release of this energy does two things. A lot of it provides an outward explosive pressure to counterbalance the inward pressure of gravity in the emerging star. This allows the star to remain stable for billions of years.