What is the concept of E=mc2?

i got this. tiny atoms hold energy that can be released by splitting the atom. is that fission? fusion? no, fission. so, the energy released (e) is always equal to the mass of the atom (m) times the square of the speed of light (c2) the (2) is supposed to be an exponent, but i dont know how to type an exponent. so the speed of light is 186,000 km/s, i think. so multiply it by itself (=34596000000) multipled by the molecular weight of the atom, is the amount of energy that comes out. ta da!