The energy on the sun is produced by what is called a nuclear fusion reaction that converts hydrogen into helium. The result of this reaction is the release of a large amount of heat and light is emitted through a process called radiation. This can also be seen in other objects such as a hot stove tops that tend to glow red as they heat up.

The sun shines because it is hot. The reason the sun is hot is because of the nuclear fusion in its core generating heat, but the shining is purely because it is hot.

The sun is a huge fire that is burning gases. As you know, fire also produces light.

The source of the sun's fuel is hydrogen and helium gases. Through a special chemical reaction, called nuclear fusion, the hydrogen gas is "burned" releasing an enormous amount of energy in the form of light and heat.

All about the Sun - Extreme science