First, the basics. To bring up V.A.T.S. you just hit the LB button on Xbox, L1 on PS4, and Q on PC. This will slow down time, but not pause it completely. Youll then see your enemies in front of you, with the system automatically focusing in on the closest one. From here you must choose which enemy you want to hit or fire at, and what part of their body to go for.
Percentages are displayed near each body part. These show the likelihood that youll actually hit it with your shot. By highlighting your target and selecting it, which can be done with the left analog stick and A/X, or clicking on it on PC, you will queue that up for one shot. This will drain your Action Points, or AP, by a select amount, so you can follow up with extra shots if you have more.
The key here is to weigh the percentage chance of hitting with the damage it will do. On the top of the screen you will see how much damage the shot will do if it lands, so if it will kill the enemy in one hit, and you have a 50% chance of making it, just queue it up twice and youre good to go. Of course, going for the head will yield the most damage, but it will also drop your chances of hitting unless you have a high Perception and some accuracy perks. Figure out what is the best combo for the enemy and go with that, or you can try to disable them.