I was amazed by this too, and even asked he site if energy was a state of matter. The conservation of energy says that matter and energy cannot be created or destroyed, just changed. So naturally you can change matter into energy. Einstein figured out that (I'm using random numbers here) if you have a block of wood with a mass of 100, you multiply it by the speed of light, and then square it, so if the speed of light is 10, (100x10)^2=1,000,000. a block of wood that equals 100 units, can be converted into energy that equals a million units. When an object is turned completely into energy, it is called total annihilation, and only happens when matter meets an equal amount of antimatter. The only problem is that antimatter isn't usually found naturally, so we can't make enough for "antimatter propulsion chambers" and antimatter bombs, and all that scifi stuff.