Ok this is perhaps the single most famous equation known to man. And I have basically zero idea how it came to be. I have a slight background in classical physics (a couple college classes) I know it states that energy is equal to mass multiplied by the speed of light squared. I have tried to read online postings on it but have been unable to follow. So is it possible to get a step by step derivation of this equation so that even a lay person could understand it?