Alrite, I'll try to give a general summary of antimatter. Antimatter is composed of antipatricles...positron, antiproton, and antineutron. The only difference between the antiparticles and their normal counterpart is the net charge, everything else is the same...for example, their mass, the propagation of light and sound and gravity, ect (hence why Simfishy said the universe would be completely the same if all the patricles would be replaced by their antipatricles). As we all know, an electon has a negative charge, a proton has a positive charge and the neutron is neutral (neutron...neutral, makes sense!

). The positron therefore has a positive charge, the antiproton has a negative charge and the antineutron is --drum role-- neutral! You might think in that case that the neutron and antineutron are the same thing, but in fact they arent. Neutrons/antineutrons and protons/antiprotons are made of quarks/antiquarks. A proton is made of 2 up quarks and 1 down quark (uud), while a neutron is made of 1 up quark and 2 down quarks (udd). The up quark has a charge of +2/3, the down quark has a charge of -1/3. The anti-up quark therefore has a charge of -2/3 and the anti-down quark has a charge of +1/3.
Proton = (uud) = 2/3 + 2/3 - 1/3 = +1
Neutron = (udd) = 2/3 - 1/3 - 1/3 = 0
antiproton = (anti-u, anti-u, anti-d) = -2/3 - 2/3 + 1/3 = -1
antineutron = (anti-u, anti-d, anti-d) = -2/3 + 1/3 + 1/3 = 0
Anways, I hope that helps you understand antimatter better. If you have any questions, just ask.
BTW, I see "IIRC" a lot, can anyone tell me what that means??