The equation stands for energy (e) equals mass (m) times the speed of light (c) squared (2), or times itself. It basically means that the amount of energy anything is capable of producing is relative to its size (mass) and the limits of physics.
Say I offer you two balls, one bowling ball, and one baseball, and challenge you to pick the one you can throw the furthest. Obviously, you're gonna pick the baseball, because the amount of energy you can exert will have a much greater impact.
Sort of like that, but with a lot of complicated math.