고 나다

'After doing X…'

고 나다 marks one action as finished before the next begins, and it almost always appears as 고 나서 or 고 나니까: 비가 오고 나니까 하늘도 깨끗하고 'after the rain, the sky was clear.' Plain -고 would just chain the two events; adding 나다 insists that the first is over and done with. 전 데뷔하고 나서 'ever since I debuted...'