Main sequence stars produce energy by burning hydrogen and converting it into helium. Because this results in the conversion of matter, a great deal of energy is released. These energies include light and other types of radiation. The radiation then streams away from the star at the speed of light.
Some stars are cooler than the sun, while others are much hotter. Hot, brilliant stars use up their fuel much more quickly than the sun. Red giants such as Betelgeuse are cooler. However, stars such as Betelgeuse are no longer in the main sequence, where stars are placed if they're burning hydrogen.
The size of the star determines what happens to it when it starts running out of hydrogen. If it's about the size of the sun, it starts to burn helium and becomes a red giant. After a few billion years, the core of the red giant cools down and expands, and the star blows off its upper layers. They form a planetary nebula, and what's left of the star eventually dies.
Stars that are more massive than the sun collapse in on themselves to the point of explosion. They turn their helium into carbon and burn other elements. They then become supernovae. Some even collapse further to become black holes or neutron stars.