Hydrogen is converted into helium
Inside our local star, hydrogen is converted into helium in a process known as the proton-proton chain reaction.
Two protons (hydrogen nuclei) collide to produce deuterium – a nuclei consisting of one proton and one neutron. In the collision, one neutrino and one positron are emitted.
Deuterium is struck by a proton and converted into helium-3 – two protons and one neutron. The fusion results in the emission of one photon, which finds its way to the Sun's surface, turning into sunlight.
Two helium-3 nuclei collide. The result is helium-4. The two protons can now enter into new nuclear processes.