The fusion process that creates helium in stars is called proton-proton chain reaction. This reaction happens in two main stages:

Stage 1: Two protons (hydrogen nuclei) collide and fuse to form a deuterium nucleus (one proton and one neutron), releasing a positron (anti-electron) and a neutrino.

Stage 2: The deuterium nucleus then collides with another proton, forming a helium-3 nucleus (two protons and one neutron) and releasing a gamma ray photon.

Finally, two helium-3 nuclei collide and fuse to form a helium-4 nucleus (two protons and two neutrons) and releasing two protons.

Here's a simplified summary:

* 4 protons (hydrogen nuclei) --> 1 helium-4 nucleus (alpha particle) + energy

This process releases a tremendous amount of energy, which is what powers stars and keeps them shining.

It's important to note that the proton-proton chain reaction is the dominant fusion process in stars like our Sun, which are relatively small and cool. In larger, hotter stars, other fusion reactions, like the carbon-nitrogen-oxygen (CNO) cycle, become more important.