Every star in the universe, including the sun, is alive due to nuclear fusion. It is through this process that they produce an enormous amount of heat and energy. The pressure at the core of any star is tremendously high, and that is where the nuclear fusion reaction occurs.
For example, the temperature at the sun’s core is around 15 million degrees Celsius. At this temperature, coupled with very high pressure, two isotopes of Hydrogen, Deuterium, and Tritium, fuse to form Helium and releases a massive amount of energy in the form of heat. Around 600 million tons of hydrogen are converted into Helium every second in the sun. The reactions which take place in the sun provide an example of nuclear fusion.