Hi. Im new to Fallout and havnt gamed much but Im having trouble killing enimies. For example I spot a scorpian or a member of the Powder Gang and shoot using vat several times. The next thing I know the bullets havnt killed the enemy[ although they have impacted] and now their closing in on me. I then try to use vat one last time but cant for some reason so i try and shoot from the hip but its to late and with one attack Im dead. Can someone advise me on what Im doing wrong? Thanks.

VATS requires you have available action points, which you've burned up if you've already fired on a target. They take a little time to regenerate. What kind of gun are you using, and where were you hitting the target? I haven't really found Powder Gangers to be much trouble with the 9mm Varmint Rifle or Pistol at the beginning. Certainly not as troublesome as Raiders in FO3 early on.

Radscorpions are another matter...

Im not sure on the gun but Im still on quest one, broc flower etc. I always go for the greatest per centage on the body. I watch the blood spurt from a perfect head shot but still end up dead. I guess I need to get used to game and how it all works as Ive only really played RDR and Mafia 2 before this.

Well even a head shot will seldom kill a target unless you are 'hidden' from him, or get a crit.
A good trick is to use vats till you run out of points... at that point you are kinda aiming at where you want to shoot anyway. Just go ahead and unload your clip into the man till he is dead.

Hmm.
Fallout =/= Realistic damage
If you run out of AP then you need to either seek cover and wait for it to regenerate and pop Jet or other AP giving chems/items.
Or you need to shoot in real time combat.

On the bottom of VATS, there's going to be a graph of enemy health. It will flash, showing you how much damage each shot will do if it connects. Make sure you've got the whole thing flashing before shooting...you should be able to get 2 or 3 shots off in VATS each time.

You just need to practice your free-aim is all. I was absolute rubbish when I started.