Hydrogen is the simplest 'normal' element so far observed. It has an atomic number of 1, and a standard atomic weight of 1.008. It is most commonly made out of 1 proton and 1 electron, although there are also isotopes of hydrogen with neutrons present.
The isotope of hydrogen with 1 neutron is deuterium. The isotope of hydrogen with 2 neutrons is called tritium. Deuterium is a stable isotope of hydrogen, however tritium is radioactive, decaying into helium-3 through beta decay. Tritium has a half-life of 12.32 years. There is also hydrogen-4, hydrogen-5, hydrogen-6 and hydrogen-7, but all of them are extremely unstable and decay in less than a sextillionth of a second!
The sun uses deuterium and tritium to generate energy, using nuclear fusion, where it uses extreme heat and pressure to fuse isotopes of hydrogen into isotopes of helium, generating energy.