This matter is called the ~Standard Model~ matter, and is a byproduct of the ~Standard Model~ of ~particle physics~, which is the most well-tested physical theory. Other theories exist, but the Standard Model is considered to be the only valid explanation for the known observed phenomena at energies in which antimatter has not been found to appear spontaneously in nature under the normal conditions of the universe.
Given the Standard Model, antimatter can be created artificially in a number of ways, of which the one thought historically to be the most powerful and promising is to first create matter, then convert it to antimatter, and then destroy both sides with a single neutron -- but doing so is much easier said than done. It has been done to a small extent (on the order of a billionth of a gram), but the amount of energy it takes to do so is enough to destroy a similar amount of matter on an atomic level (or possibly even a nuclear level). The lack of antimatter in the absence of interactions with normal particles suggested the idea that antimatter possessed a negative charge. While that is true, there is no evidence that this charge can be observed in the real world -- the evidence is just that it is conserved. Nevertheless, antimatter is an important part of some theories in particle physics, in particular the dark matter theory which proposes that particles which are not readily detected by our current instruments are the baryonic matter in the universe.
Other theories suggest that matter and antimatter have the same amount of mass (unity), but different charge and hence different electric or magnetic properties. In these cases, they would annihilate each other. The most promising one in that direction is supersymmetry, which implies that every particle is accompanied with a particularly heavy partner -- called the [[supersymmetric partner|supersymmetric partner]] -- which has the same amount of mass and a different charge. This works fine, until the superpartner of a particular particle is created, then the other one annihilates the other. d2c66b5586