First things first, I'm not from the USA and I'm pretty sure careers don't work the same as in my country, but since I'm going to study there I'd like to know what should I study to become a HR manager. I know it won't be immediate and that, in order to became one, I'll have to work at the department for quite long and gain work experience, but overall I have no idea what kind of career should I look for to work in that sector, so if you could tell me something about it I would really appreciate. Thank you in advance.

I think personnel management is the way to go.  Also you can study any course in the management field then go for any personnel management professional course that often offers by professional bodies.