Point of View (POV) specifies through whose eyes the story is being told.
First person – When you write using I, we, me, mine and my, the story is being told by the protagonist (central character) in first person.
Call me Ishmael. Some years ago—never mind how long precisely—having little or no money in my purse, and nothing particular to interest me on shore, I thought I would sail about a little and see the watery part of the world. Opening line of Moby Dick by Herman Melville.
Second person – Probably the rarest writing mode is second-person narrative, in which the narrator turns the reader (you) into a character.
You don’t know about me without you have read a book by the name of The Adventures of Tom Sawyer; but that ain’t no matter. —Opening line from Adventures of Huckleberry Finn by Mark Twain.
Third person – Most novels are written in third person narrative mode using he, she, it, and they.
It was the best of times, it was the worst of times, it was the age of wisdom, it was the age of foolishness, it was the epoch of belief, it was the epoch of incredulity, it was the season of Light, it was the season of Darkness, it was the spring of hope, it was the winter of despair. Opening line from A Tale of Two Cities by Charles Dickens.
The reason most novels are written in third person is because 1) it is arguably the easiest style in which to write, 2) it tends to be more objective, 3) it gives the writer more freedom to introduce information, 4) the narrator knows everything there is to know about the characters, and 5) it keeps the focus on the protagonist and what he/she knows, feels and experiences.
But there’s more to know about third person. There’s third person limited where the narrator knows only the thoughts and feelings of a single character. In other words, the reader will not know more than the main character. And then there’s third person omniscient where the narrator knows the thoughts and feelings of all the characters.
Writing with multiple POV’s appears to be acceptable by most experts if done properly and if it is indeed necessary to the story. If the switch isn’t done effectively, the reader will become confused. My advice for first-time writers is to stick to one POV.
The following sentence exemplifies a confusing change in POV.
Winnie’s stomach lurched the moment she saw him, but Harold’s excitement was hard to contain when she split from the crowd and walked in his direction.
Winnie is the protagonist, so how would she know that Harold was excited at the thought of meeting her. That would be getting inside his head, not hers.
The most important rule is to be consistent. Once you pick a POV, stick with it throughout the entire manuscript.