In practical terms, there are three points of view, first person, third person limited, and third person omniscient.
First person is the I form.
I woke up in bed and discovered that I was sharing it with the entire line-up of One Direction.
It is useful for diary type stories, or stories which revolve around the adventures of one character.
Under no circumstances can you switch POV when you are using First person. You can not have the previous line followed by
<Harry Styles POV>
I woke up in a strange bed and found I was sharing it with an under-age high school nerd.
Third person omnescient is the story told through an all-knowing narrator.
Once upon a time, there was three bears who lived together, in spite of the fact that none of them were gay.
It is useful for chidlren's stories, biographies, battle scenes, stories with a large cast of characters or the book of a film.
The advantage is that you can tell the reader everything that is happening in the story.
The disadvantage is that it can be hard for the reader to get absorbed in a TPO story and it is harder to mislead the reader.
Third Person Limited This is third person but told from inside the head of one or more characters. He felt the bullet hit his arm. Pain swamped him, driving him to his knees. Why had he thought he could do this?
The advantage is that is is very intimate. The reader sees, feels, hears and suffers as the hero does. The reader gets involved with the character very quickly. It also gives the option of switching POV to another character and letting the reader into her head too.
The disadvantage is that you are more limited in what you can tell the reader. If your POV character doesn't know something, the reader can't either.
Other Points of view There are other points of view like second person, "you ran away, frightened." or first person plural, "We ran away". You can see why they are not usually seen in commercial novels.
Head Hopping.
The author can't decide which character should have the POV, and keeps jumping from one character to another. It is normal for one character to keep POV during an entire scene. This rule can be bent, particularly during love scenes. Typically, you drop down a line to indicate that a new character now has POV.
Do not switch POV every couple of paragraphs.
As a general rule, POV belongs with the person who has the most at stake in a scene. If a bully is beating up a kid, then POV would normally be with the kid getting his face shoved down the toilet. You might show the bully unable to leave the kid alone, even though he knows it's going to get him expelled. You would not give POV to the woman watching from the car across the road.
Point of view shifts This is where the POV character knows what other characters are thinking, feeling or seeing.
He admired the heroine as she came down the stairs. Her eyes were moist with anxiety and her shoes pinched her feet.
In this case, the hero can't know that the heroine is anxious, or that her shoes hurt. He's not a mind reader. All he can see is her eyes are moist and that she is limping.
Remember, third person limited is from inside the POV character's head.
A more subtle version is when the hero mysteriously knows the other character's feelings.
InfodumpThis is where the author has a lot of things she wants to tell the reader, although the reader usually has zero interest. Indodumps are bad, and using POV properly is a good way to avoid them.
Your POV character, whether first or third person, should only think things which she would naturally think.
She would not walk into her kitchen and notice that it has cream-coloured walls, a microwave which runs by electricty, a fridge which contains CFC gases and taps which bring water from the recycling centre. She will notice the blood on the floor and the broken window.
Your POV character must not spend her time explaining the set-up to the reader. You don't think, "I'm off to meet my best friend, who I met in kindergarten when he pulled my hair and I stole his Peppa Pig lunchbox..." You think, "I hope Pete remembers to bring that tenner he owes me." So your POV should not to this either.
