This expression, when added to a verb stem, expresses the finishing of one behaviour (V), followed by the start of another.
Note that this grammar structure is not used with motion verbs such as 가다 and 오다.
숙제를 하고 나서 쉬었어요.
I rested after doing my homework.
아침에 일어나고 나서 샤워를 해요.
After getting up in the morning I shower.