Smoking any amount of cigarettes is not good for your health or lungs and even smoking just one cigarette is not healthy.
But to really mess up your lungs you'd need to smoke several packs of cigarettes over around 5 to 10 years and sometimes you may smoke for 20 years or 25 years and then you may get your lungs messed up enough to get COPD.
But all the time that you're smoking cigarettes you're doing your lungs harm and damaging your lungs because you'll notice that you'll start coughing a lot which means that you're having lung problems.
Smoking is very harmful to your health and you should never smoke any cigarettes at all and if you haven't started smoking cigarettes you should never start smoking even one cigarette and if you're already smoking you should do your best to quit smoking cigarettes.