Genre:
The major category into which a literary work fits. The basic divisions are poetry, prose, and drama. However, subdivisions may also be called genres, for example: novels, short stories, essays, autobiographies, etc.

Example:
"When he found i would leave him, he took care to prevent my getting employment in any other printing-house of the town..."
-Autobiography of Benjamin Franklin

Explanation:
This shows that the genre of this novel is an autobiography, because Franklin wrote the novel himself, hence the first person point of view. The purpose of this is to take a certain time in one's  life that was interesting or holds great significance and tell it from their own point of view. This is important because the reader wants to hear the facts from the person they are learning/reading about. The purpose of the genre of a book helps the reader know how true the facts are, and what type of book they will be reading. If they want the most facts possible they would read his autobiography, not a child's picture book.