I don't think it would make a difference, except positive would be negative and negative would be positive. From our perspective.
Antimatter is the opposite of matter, kind of like the equivalent negative number, but only if they violently exploded when combined instead of just being zero. (It does end up as zero, but after the violent explosion.) It makes up antiprotons, antielectrons, and antineutrons, which are like the ones we have, just with the charges flipped. (Except for neutrons, which don't have a charge.) Antimatter isn't very stable in our universe, because seeing as how it's made of matter, it gets annihilated very quickly. In a world of antimatter, it's stable, and more or less would just from the same elements and thus the same structure that our universe does. Except with the charges flipped from our perspective.