to smoke a cigarette; to inhale tobacco smoke (common everyday expression).
飲み会のあとで、外に出てタバコを吸う人が何人かいた。
After the party, several people went outside to smoke.
病院の入口に『タバコを吸うな』という看板が立っている。
There's a sign at the hospital entrance that says 'Do not smoke'.
禁煙しようと決めたが、ついタバコを吸ってしまった。
I decided to quit smoking, but I ended up smoking anyway.