When to use to congratulate in Korean
Korean: 축하하다[ chuk-ha-ha-da ]

When to use it
The word (축하하다) means to congratulate someone or celebrate a happy event. You use it for birthdays, weddings, passing a test, getting a new job, and other good news. In Korean, it is often used with the thing you are celebrating, like a birthday or graduation.
Example sentences
생일을 축하해요!
Happy birthday!
가족이 집에서 내 생일을 축하해요.
My family celebrates my birthday at home.
선생님이 학교에서 제 합격을 축하했어요.
My teacher congratulated me on passing at school.
우리는 공원에서 친구의 결혼을 축하했어요.
We celebrated our friend's wedding in the park.
꽃집에서 언니의 졸업을 축하하려고 꽃을 샀어요.
I bought flowers at the flower shop to congratulate my older sister on her graduation.
여행 중에 호텔에서 부모님의 결혼기념일을 축하했어요.
We celebrated my parents' wedding anniversary at a hotel during our trip.