A writer can choose first, third or even second person to narrate a story. First person is typically covers one point of view, and the reader is limited to what the narrator knows. This approach is often employed in biographies and fictional stories. "I was born in a shack in Oklahoma and homeschooled by my grandmother" is an example of first person. The third-person narrator makes readers aware of story elements the characters might not know. An example of third person: "He was born in a shack in Oklahoma and homeschooled by his grandmother." Used less frequently is second person: "You move through the crowd and see a light at the end of the tunnel." Second person expresses more immediacy in the storytelling and is frequently used in screenwriting.
The linear narrative is used when the author wants to tell a story in the order it happens. This means starting at the beginning and stopping at the end, without telling any of the story events out of order. That does not mean narrative in linear order cannot include events that happened before the story. These are often introduced using another narrative strategy called "flashback."
The flashback strategy clues in readers to something that happened before the story begins. Readers gain insight into character personality or motivation. Flashback introduces events, often through character memory or dreams, that are important to a story but not part of the present time in the story. Authors may use a flashback to have a character remember a childhood fear that plays an important role in the story. By introducing these elements through flashback, readers understand more as the story unfolds.
An author uses nonlinear narratives to keep some story elements from the reader. For example, a nonlinear murder mystery may begin in the present with the crime and then dramatize events leading up to the crime. Nonlinear moves freely back and forth between past and present. This is not a flashback, which details a past event through memories or dreams. With flashback, one character's point of view is the foundation for the narrative. Everything in the flashback is from that character's point of view. With nonlinear storytelling, the author employs several perspectives and writes about events that the characters of the story may not know.