Here's a breakdown of how it works:

* The Fuel: Stars are primarily composed of hydrogen.

* The Process: Under immense pressure and heat in the star's core, hydrogen atoms fuse together to form helium. This fusion releases an enormous amount of energy, which is what makes stars shine.

* The Energy: The energy released in nuclear fusion is in the form of light and heat. This energy travels outwards from the core, eventually reaching the star's surface and radiating into space.

Key points about nuclear fusion in stars:

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

* A small amount of mass is converted into energy. This is described by Einstein's famous equation, E=mc².

* The process is ongoing, providing a continuous source of energy for the star.

* The type of fusion reactions that occur depend on the star's mass and temperature. Heavier stars can fuse heavier elements, like carbon and oxygen.

Nuclear fusion is the fundamental process that sustains stars and provides the energy that powers the universe.