The sunn is started by a nebula or a cloud of dust and gas. Gravity pulls the dust and gas into a ball, which then gets incredibly hot and dense, hot enough to start fusion of hydrogen. Fusion is the process of joining two nuclei together which, in the sun's place, is hydrogen nuclei, thus ctreating intense heat that turns the hydrogen gas to plasma, a state of matter where electrons are ripped off atoms. The hydrogen is the "fuel" of the sun, and if the sun runs out of hydrogen it will die in an explosive process known as nuclear flash. The waste product of the of hydrogen nuclei is helium, and it's building up in the sun until it dies.