~았/었더니 (Used with verbs)

Realise or notice something after doing something:
오랜만에 고향에 갔더니 많은 것이 변해 있었어 – When I visited my hometown, a lot had changed.

The result (second clause) of doing something (first clause):
어제 술을 많이 마셨더니 오늘 머리가 아파요 – I’ve got a headache because I drank a lot yesterday.
내가 공부를 열심히 했더니 성적이 올랐다 – Since I studied hard, my grade went up.