"What is Helium" is a bit of a strange question. It is an inert (or noble) gas that consists of 2 protons and a slightly varying number of neutrons, though the only two stable isotopes (Atoms with the same number of protons but a differing number of neutrons) are Helium-3 and Helium-4, with 1 and 3 neutrons respectively. It is the second lightest element, as well as the second most abundant in the Universe. It is found in large quantities inside stars, such as our sun, due to the fact that is made during nuclear fusion. Please let me know if there's anything in particular you'd like to know about it.