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I think is a bad fit for MO. Why not tex.stackexchange?
The answer to almost all of them is "spacing".
I don't think that as asked the question is a good fit for the SE network (to be clear, I'm thinking about its fitness for TeX-SX, I don't think it would work in any way on MO). I think that the best strategy would be to set out to write a blog post about this and to ask specific questions when you find that you aren't able to figure something out for yourself. A lot is in the AMS guides, and more in standard typographical references.
Regarding what the actual differences are (there's some information as to why as well), here are some questions on TeX-SX where you could start reading.