What are some nuclear reactions that occur to produce heat and light on the sun?

The reactions that take place on the sun are nuclear fusion reactions. Stars are, after all, giant nuclear fusion engines. On our neighborhood star, hydrogen is being fused into helium in the proton-proton chain. In this reaction, two protons are fused and one of them undergoes a beta decay to become a neutron, producing deuterium. There are a couple of different ways the fusion reactions can go from there, but helium eventually results. The process by which stars "run" is called stellar nucleosynthesis, and you can use the links below to investigate further.