됐던

In a sentence

• 어제는 날씨가 정말 좋았고, 내가 갔던 공원도 아름다웠던 곳이었어요.

  Yesterday the weather was really nice, and the park I went to was also a beautiful place.

  Here, '됐던' is used as the past tense form describing the park as being beautiful in the past.

• 그 친구가 예전에 대통령이 되었던 적이 있었습니다.

  That friend once became the president in the past.

  '됐던' here conveys a completed action or status, indicating the friend's past experience of becoming a president.

• 떨어졌던 물건을 주워 올려놓았습니다.

  I picked up the item that had fallen and placed it back.

  In this case, '됐던' is part of the descriptor for the item having fallen in the past.