One question I see over and over(and over and over and over and over and over....) on writers' boards is "Which POV should I use?"
It's not a stupid question by any means, and I'm not going to belittle anyone for asking it. It's one of the first questions you have to answer when you start writing a piece and the answer may even change before you're finished. The "wrong" part of the question (which is more inexperience than wrong) comes in believing that someone else can answer this for you.
You're the only one who knows your characters and their story. You know who's in what scene and who isn't. I'm going to *try* and demonstrate the difference between 1st, 2nd, and 3rd, (and hopefully not make a total idiot out of myself in the process).
Let me start with 1st person and what it isn't. 1st person isn't an excuse to filter everything through the MC's eyes, ears, and fingers. Yes, they're loaning your their thoughts for the duration of the story, but as a writer you need to get out of their head.
Think of it like an announcer at a ballgame. They don't shout "I saw the ball caught at the last second!" No, they're busy watching balls and bats and bodies to filter anything. "He's running backward, toward the wall. It's gonna be close. Maybe... maybe... could it be.... He did it! He caught the ball right at the wall. What a play!"
What 1st is especially good for is an intimate look at a character from close up when you want the reader to tag along for the whole experience. You've given them a fixed camera and that's all they can use to see and hear what's going on.
2nd person is the "oddball" POV. It's a more distant voice, transferring feeling and responsibility to a 3rd party - stage direction where you pick up the reader and shoe horn them into the story. Voice is always key, but moreso with 2nd because if you screw it up here, you lose the reader faster. In 2nd person, the reader agrees to play a part and assume the identity of your character; they're now a method actor. You know that almost cliche of "What's my motivation?" Well, screw up the voice in 2nd person, and that's where your reader's mind will go. Done well, and most can accept playing along with a character, even if it's one different from their own appearance, goals, or morals. But the instant you breach the character's appearance, goals or morals, you're done. No one wants to be a bad actor, and they k-n-o-w know that the character wouldn't do/say/think what you wrote. If they character won't do it, then neither will they.
3rd person is the "safe" voice. That's not to say it's the easiest, but for those with difficult subject matter, it's the one that puts the most distance between the reader and characters. There's a definite line that tells the reader they're not in anyone's shoes, but rather learning about them. You can use 3rd close, which fixes the POV of one character, or 3rd omni, in which your narrator sees all and knows all, but neither of these gives you an excuse to head hop at will.
So, that's it. My contribution to the definitions of POV.
There's no magic formula that will make your choice "right"; it's determined by the needs of your story. Contrary to popular belief, YA can be written in 3rd person close; 3rd omni, or even 2nd person and still work. Adult lit can be in 1st. The story decides. It's as simple as that.