Antimatter are just opposite to matter. For example antiparticle of electron is positron(not proton) has just opposite electric charge. Antimatter has property just opposite to matter.
One would expect the Big Bang to produce equal amounts of matter and antimatter, and, since the two annihilate one another on contact, this should have led to a universe with no particles, filled only with radiation.
This problem can be solved if there exists some process that favours matter over antimatter, leading to the excess that we see today.