다녀오고

In a sentence

• 나는 학교에 다녀오고 지금 집에 있어요.

  I went to school and am now at home.

  Here, '다녀오고' indicates an action of having gone to school and returned. It's used in the present perfect tense to connect past actions with the current state.

• 엄마는 시장에 다녀오고 저녁 준비를 하고 있어요.

  Mom went to the market and is preparing dinner.

  In this sentence, '다녀오고' suggests that the mother visited the market and, having completed that, is now engaged in another activity.

• 친구는 도서관에 다녀오고 나에게 책을 빌려줬어요.

  My friend visited the library and lent me a book.

  '다녀오고' is used to describe the prior action of visiting the library as a background for the friend lending the book.