The Sun was formed some 5 billion years ago from interstellar material, which is not evenly distributed, but is rather in the form of clouds. When gravitation slowly condensed the particles of this cloud, a so-called primitive sun was born. An orbiting disc of the same particles formed around its equator. Both the primitive Sun and the disc continued to compress. Due to the compression, the size of the gas cloud decreased to a fraction of its original size, and as the pressure increased, it heated to an infrared radiation releasing protostar.
The gravity caused the protosun to continue compressing, and as a consequence, its core heated. When the core had reached a temperature of 10 million degrees Celsius, a major change took place. Nuclear reactions began and the Sun lit up. Thus the Sun entered the main sequence phase, where it still is.
Today our central star is approximately halfway through its steady main phase. We still have 5 billion years left to enjoy the Sun's gentle warmth.
