Hydrogen and helium are found in all stars. Ninety percent of all atoms in the universe are hydrogen atoms and fusion reactions fuel stars, resulting in the formation of helium and higher atomic number elements.
The most common elements, like carbon and nitrogen, are created in the cores of most stars, fused from lighter elements like hydrogen and helium. The heaviest elements, like iron, however, are only formed in the massive stars which end their lives in supernova explosions.
