There are two forces that govern our universe and allow stars to create the elements on the periodic table: the strong nuclear force and the weak nuclear force. The strong nuclear force governs nuclear stability of atoms and allows for fusion, the process by which two atomic nuclei come together. Conversely, the weak nuclear force governs the nuclear instability of atoms, which results in radioactive decay and also allows for fission (the splitting of atomic nuclei). The creation of all elements in the universe, besides hydrogen, depends on the collaboration between the strong and weak nuclear force.
A star is born when the weak nuclear force transforms the protons in a hydrogen nucleus into neutrons. This is necessary because fusion cannot occur between two atomic nuclei if both contain a positive charge, as opposite charges attract while like charges repel each other. This process continues in the star’s core as particles called gluons use the strong nuclear force to fuse more nuclei together. Overtime, fusion will create more and more complex elements that have higher atomic numbers and are further down on the periodic table. For example, hydrogen will fuse into helium and helium will fuse into beryllium.
Although nuclear fusion generates immense amounts of energy in the form of light and heat, it also needs energy to continue fusing atomic nuclei together. When a star creates iron in its core, it takes more energy to fuse the nuclei together than the amount of energy the fusion process creates. Therefore, the star eventually exhausts its fuel. When this happens, depending on the size of the star, a nova or supernova will occur, in which the star will spread the elements it created throughout its lifetime across the vast universe.