Matter is fairly explanatory; antimatter, though, is harder to conceive of. Antimatter is the same mass as matter yet with an opposite charge. But why is it so hard to make and contain it? MinutePhysics explains.
Every particle known to man has an opposite, yet equal, version of itself. It helps to think of this concept as being like opposite and negative numbers. When positive one and negative one are combined, they cancel one another out. Interestingly, this is what matter and antimatter does as well. Fortunately, there seems to be more matter than antimatter in the universe. Otherwise, the two would constantly be annihilating themselves and potentially causing some real damage. This is why many scientists have postulated that antimatter could be the key to creating some truly devastating weapons. Antimatter poses one big question. If matter and antimatter are identical mirror images of each other, why did the Big Bang producer so much more matter than antimatter.