"Mmmn. The first thing to know about guns is that you never want to point them at someone. Always up in the sky when you're not pointed in the direction of your target." he said. It wasn't a rule of thumb once you were a gunman, but he doubted that Katara was going to start fighting with guns, so giving her the 'shooting range' version of gun safety would be okay for now.
Vincent picked up out of the bag a small silver gun, and lightly presented it to her. "This is what we would call a 9mm. A fairly standard low powered hand gun. It'll be easier to learn on. And this..." he held up a golden looking bullet, though Katara might recognize it was made out of brass rather than gold. "is a bullet. this is what is fired out of the gun, and will go into someone when you aim and fire at them."
Quietly, Vincent stepped around behind Katara, and lightly showed her how to hold the small pistol. Pressing up against her back, he rested his hands on her forearms, so the kick from the gun wouldn't make her lose control. "Now, it's going to make a loud noise when you pull the trigger, and fire the bullet at that tree over there..." he said softly into her ear. "Give the trigger a light squeeze, and remember to grip the gun firmly because it's going to jump a little when you fire it..."