How is hydrogen involved in the production of heat and light in the sun?

Answer 1

1H¹ + 1H¹ = 1H² +.0015482862c² (includes 1electron)
1H² + 1H² = 1He4 +.0256003063c²

or a total of about 0.0286968787c² energy for each H to He fusion.

That's 645,680 joules per gram of hydrogen.

At those energy levels, it is not possible for atoms to form, so some helium nuclei (alpha particles), electrons (beta particles) and energy (gamma rays) is emitted from the Sun. These energies are converted into heat and light by repeated collisions with other atoms, sometimes in the photosphere of the Sun, and sometimes in our ionosphere or atmosphere. Some even reach the surface and impact on us directly.