Fallout 4 is my first Fallout game. I thought I understand the V.A.T.S? thing before I went into the game but I'm defiantly doing something wrong.
I'm playing on PS4, btw

Okay so I know that you press L1 to activate it and from there you can chose which part of the NPC's body to shoot at. Press R2 to lock on and press X to shoot. That's as much as I understand. If I press R2 again then I can create a second bracket. Y'know, the one that appears wheb you lock on. What does that mean? I can also lock on to two different body parts at once but it doesn't seem to make a difference when I shoot.
And those numbers... what do they mean?

When I've locked onto something and shoot, my character will shoot once and nothing happens. Then I return to normal gameplay. This could be because I'm often faraway from the NPC's when I try this but just today I went right up to an enemy, locked onto his head and shot. The bullet hit and there was a splat of blood but he was still alive. I hit perfectly hit his head. Do head shots not count in this game?

I did manage to figure out that you have to hold the R2 button during the cinematic part but that doesn't work for weapons like pistols. I've seen people on Youtube make these really gory finishes but so far I haven't been able to make anything like that happen.

I'm sorry the answers to some of these questions are obvious. Again, Fallout 4 is my first Fallout game and it never explains how these things work. If I hadn't seen previews of the game, I probably wouldn't even know the V.A.T.S. exist.

A quick breakdown of VATS.

The numbers are your % chance to hit in VATs. So it's a good idea to aim for one of the higher numbers or risk the headshot. Headshots do more damage but they are not auto kill.

To get something gory there is a perk under Luck (level 3) called bloody mess which gives a chance for things to explode when you shoot them. That is normally what causes the mess.

I'm running a PS4 so yes Hit L1 to go into VATs, and then when you select R2 it puts the box on that location. That is the first shot. You can keep hitting R2 and put multiple boxes around it, which it will shoot once for each box around the location. It may stop shooting but only if you kill it. Your AP is the limiting factor on how many shots you can take in VATs.

@FiannatTiger So when using weapons like pistols, do you have to press anything while the animation is playing out like with automatic weapons?

No. When you have enough ammo in the gun it will shoot multiple times. Once you hit X to confirm, you just sit back and enjoy the animation. The only thing you might want to hit is the Square button if you have your critical meter full it will execute a crit.

1 time time use could be the weapon your using, like the wind up musket, sometimes he will wind up in slow mo and shoot but never seem to do it more than once. I still havent figured out the execute critical option myself and sadly I have played them all