The sun reaches a state of equilibrium. Millions or billions of years later as the hydrogen becomes used up, the outward energy decreases, and the sun begins to contract further. At some point, so much further heat is created by the further squeezing that helium atoms start fusing into carbon atoms. For a shorter period it stabilizes in size again, but then further contraction again begins as the helium is used up. The different ways that suns die is another fascinating subject, for another time.
Stars frequently form in groups.
There are places in the sky where you can see this process occurring. Nebulae are some of the most beautiful objects in space to observe with a pair of binoculars or a telescope. With binoculars or a small telescope it appears as a glowing cloud with bright stars inside that light it up. The remaining clumps of gas are still contracting to form more stars. This is a stellar nursery, a star cluster in the making, in which a whole litter of stars is being born.