As was written, a particle and its antiparticle have the same mass as one another but opposite electric charge and other differences in quantum numbers. That means a proton has a positive charge while an antiproton has a negative charge, and therefore they attract each other. A collision between any particle and its antiparticle partner leads to their mutual annihilation. Since matter and antimatter carry an immense amount of energy (due to E = mc2), their mutual annihilation is associated with producing intense photons (gamma rays), neutrinos, and sometimes less-massive particle-antiparticle pairs.
See also: Antimatter