Could someone help me? I'm having trouble understanding E = mc^2.... (READ THE DESCRIPTION!!!)?

About Energy = M times the Speed of Light squared...... Yeah, I don't get it. How did Einstein come up with the equation, and what does squaring the product of the speed of light and the element's m have anything to do with finding the energy, in joules, of nuclear fission. I'm totally lost. Could someone explain this to me REALLY SOON?!!? Thanks!