Here's a simplified explanation:

* Hydrogen (H) is the Sun's primary fuel. It's made up of single protons.

* Fusion is the process where atomic nuclei combine to form a heavier nucleus.

* In the Sun's core, intense heat and pressure force hydrogen nuclei together.

* Four hydrogen nuclei (protons) fuse to form one helium nucleus (2 protons and 2 neutrons).

* This process also releases a tremendous amount of energy in the form of light and heat.

This process, called nuclear fusion, is what powers the Sun and gives it its energy.