Antimatter is basically matter’s evil twin. Most of the stuff in the universe (as far as we can tell) is matter, namely electrons, up quarks and down quarks. Antimatter is very much like matter, except for a few key differences which I’ll get back to. Antimatter particles like antielectrons and antiprotons interact with each other in the same way normal matter interacts with other normal matter. Antiparticles have the same mass as their corresponding particle, and thus respond to gravity in the same way. The differences begin with quantum spin, angular momentum contained by fundamental particles. Antiparticles have a quantum spin equal to the opposite of the spin of their corresponding particle. Antiparticles also have the opposite electric charge of their corresponding particle, which means an antielectron has a positive charge and an antiproton has a negative charge. So what happens when matter and antimatter interact? Not much, but since they oppose each other in charge and are subject to gravity they will likely collide, and when matter and antimatter collide they annihilate each other. The total mass of both the particle and antiparticle is converted directly into energy in the form of gamma radiation, and if you could get a kilogram of matter and a kilogram of antimatter to annihilate each other the energy released would be equal to the amount of solar energy that reaches the Earth in one second.