Some writers latch on to what Point of View is immediately. Others aren't quite sure what it is or how to deal with it.
Actually, they're probably overthinking what it should be, which is simply the writer being in the mind of just one character.
It can be done in various ways in the text. For instance, it's easy to stay in one character's head if the presentation is in 1st person, that is, the character is telling the story himself or herself. The reader doesn't know anything that the character doesn't. Not what others are thinking or what they are doing if the character telling the story can't physically see them or hear them. An example of 1st person presentation is Jim Butcher's Dresden Files and a number of other urban fantasy stories. The hero is the character all information feeds through and from.
Another way to do a single character POV yet write in the 3rd person is to only show the writer what the main character sees and hears though they aren't the one telling the story. Although she occasionally has a short section wherein her main character isn't present, for the most part all seven of J. K. Rowling's Harry Potter series are told with information fed to the reader only though events in which Harry is present. Ron doesn't have a POV and neither does the brilliant Ms. Granger.
The most common presentation in a novel is one in which more than a single character feeds the reader information. And by this I don't mean that the presentation is in 1st person, it's in 3rd person and readers simply follow one character for a few pages or for a chapter. They see what this character sees, hear what they hear, and know what they think, what they might be planning to do, see decisions being made whether for good or for bad. Then the writer switches to a different character for more of the same, but from a different Point Of View.
Point of View is what a character sees, hears, does, and thinks.
The trick is to ensure that what another character thinks doesn't seep in. The best way to do this is simply put yourself in the POV character's place, in their head, and stay there for the duration of the scene, or section -- however long it is until another character takes the helm.
Beware of "head hopping" though. This was once a popular presentation but it isn't any longer. Head hopping is when one scene has the POV of two or more characters in it. It can be confusing to know who is thinking what at times. So -- DON'T DO IT! Stick with one character at a time.