The core aspects for defining stars is basically when tons of plasma are held together by self-gravity, but a star's actual life starts when nebula(tons of random materials mixed together called intersteller medium) starts to have an gravitational collapse. Which then releases many chemical elements and materials that help start the stars life.

Stars serve an extremely important purpose, whether it be being the reason why most of the elements we know on the periodic table being because of stars, heat from suns giving live to various planets, or even holding many planets in orbit to create planetary systems.