explain antimatter

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How do matter and antimatter annihilate?
Why is antimatter opposite charge and not opposite mass or spin? Why don't opposite spin electrons annihilate?
What would be the difference between an antielectron and a positive electron that wasn't antimatter?
Why can't charges from e+ and e- annihilate independently from the rest of the particle and leave a couple of uncharged electron mass particles?
How are photons their own antiparticle when they don't have charge? What happens when a photon and antiphoton annihilate?

They're all confused about where all the antimatter from the big bang is but couldn't it be spin is the real antiproperty and we have equal amounts of matter and antimatter?