What is the difference of narrator and author of a text?

The author is whoever writes the book.

The third person narrator would be someone out side the story who narrates it. An example of a third person narrator is "As Emily was fretting over her test, she secretly thought, 'I wonder if I can cheat on this?'" (This is third person limited)

There are three kinds of the third person point of view. There are

-third person limited

-third person omniscient

-third person objective or camera

Limited: The narrator can relate the thoughts and feelings of only one character

Omniscient: The narrator can relate the thoughts and feelings of all characters

Camera: The narrator tells the story from a neutral point of view, similar to a newspaper article.