I just started the game. What do you have to do to start using VATS? When i push the button i just hear a click like shooting an empty gun.

Well you need to look at a enemy for starters.

You need to get the pip-boy first and have an enemy in range.

Well technically you can summon vats mode without a enemy if you hold down the vats button, but unless you have the VANS perks its honestly useless to do that.

True, but I would never suggest that perk to anybody.

its the enemy in range, that was simple