Shemale, trans - male transformed into a female by going the hard way, but keeping the penis. Surgery+hormones and stuff like that.
Herm - human or animal, that has genitals from both genders and can look like either of genders(a girl with vagina and penis or a guy with same set of tools).
Futanari - a woman with vagina and penis, always look like female and has two variants of her genitalia: a penis growing where the clitoris usually would be, with balls or no balls.
As for how to address them... Transsexuals are "she" and I think it's actually official.
Herm? Dunno, I think it depends on how they look like and want to be addressed.