시작한

In a sentence

• 그는 새로운 프로젝트를 시작한 상태이다.

  He is in the state of having started a new project.

  Here, '시작한' is a participial form describing 'the state of having started'.

• 그들이 시작한 행사가 큰 성공을 거두었다.

  The event they started became a great success.

  In this sentence, '시작한' is used as a modifier for 'event', indicating it was started by 'they'.

• 나는 오늘 아침에 시작한 책을 아직 읽고 있다.

  I am still reading the book I started this morning.

  Here, '시작한' modifies 'book', specifying that it was the book the speaker began this morning.