explanation.

[gilded shoal]

when saying ”i“ do u always say “나는“ / ”저는“ or is it different per sentence.
like 저는 학교뒤에 있어요
would that be correct or?

[whole tusk]

나는 is me for informal and 저는 is me for formal

That’s the only difference and there is no other word for it

You either say those two or just put no word for I at all and leave it up to context