In Japan would you call somone by there first name or last name?

Question:

It's for a story im writing & i want to use some japanese styles and stuff ...
like for example my main character in my story's name is Nagisa(her first name) Sakura(her last name)
so would it be Nagisa Sakura or Sakura Nagisa
And could someone explain it 2 meh plz & thank yuh >:3

Answer:

It should be Sakura Nagisa.

How others call her, depends on who's calling her.

In formal relationship like business, they would call her with her last name with -san like Sakura-san.

In very casual relation like from her BF or close friends, they would call her Nagisa, first name.