Characters:

Characters are the main people in the book.  The people in the book are the characters.  Anne Frank is the main character.

Themes:

Themes are Coming of Age, Identity, Suffering, War, Duty, Virtue, Anti-Semitism are a few.  Themes are issues that the author choose to explore in the book.

Author's approach:

The book is a diary, a journal by Anne Frank.  It is written privately, not for an audience, as a recollection and recording of the details of her life.  In it, she journals her thoughts, feelings and opinions about subjects that are important to her.

Style of Writing:

The style of writing is how the author choose to write to the audience and the voice he/she uses.  Anne Frank was not writing to an audience.  She was writing to herself in her own journal.  Her voice was the unassuming voice of a teenage girl writing down her thoughts to herself.

The development of the plot is the progression of action and solving of problems throughout the story.  In this case, they were real life problems that Anne was trying to solve herself.  The book ends abruptly with no completion or resolution because Anne's family was taken by Nazis, presumably, and Anne's diary was left behind as her own record of her short life in Germany occupied Netherlands during WWII.  There was no one left to finish the story--Anne was gone.