I dont understand Spirited Away

Is the movie subjective, or is there an actual explanation? Is the world Chihiro goes to in her head? Is it just something she imagines to grow confidence and to get ready to grow up? How long did it all take? Did any of the things really happen in their real world? Im very confused. Also is Haku real? Why would his real name be Kohaku, the rivers name? Id appreciate any answers from someone who knows.

Edit: Thanks for most of the answers