Well welcome to the Zone!
If you're going to be in the Zone, there are a few things I recommend first.
-Start with Shadow Of Chernobyl. A lot of people say that Call of Pripyat is the way to go; but if you do the story can be all convoluted and you could miss a lot by not play Chernobyl first.
-Play on Master difficulty. Why?! Because Master difficulty isn't like other games. Sure, your enemy may be able to kill you quickly, but that also means you can kill them just as fast! If you lower the difficulty, it takes longer for you to die, but your enemies become bullet sponges as well!
-ARGH! Alex! None of my targets are dying when I'm shooting them! Well thats to be expected in the very beginning of the game. The weapons you receive right off the bat have terrible accuracy and are only good in close quarters.
Don't run and gun! It's not that kind of game. Stop. Take your time. Aim carefully and don't try to move your mouse too much when shooting. The bullet physics are actually well done and react to how you move your mouse/gun before you pull the trigger.
And finally, Mods! You need them. Unfortunately, CSC was dissolved and had to put out a game with many bugs and issues. Below, I've attached a Stalkers Quick guide that you can use to get the correct mods and show you what to do.
Enjoy!