I am 24. I have the habit of smoking.?

But I don't smoke excessively; two or three cigarettes a day. I am trying to stop it. But I am not able to stop it. If I feel like smoking, I can't help not smoking. Am I addicted to smoking? What should I do to quit it? Is it normal among youth to smoke? Most of my friends don't smoke. I am surprised how and why I got into this habit while most of my friends do not have this habit.