If, when, once

엑소를 만나면 난 행복해요 –  If I meet Exo, I will be happy.  
나는 기분이 좋으면 춤을 춰요 – I dance when I’m in a good mood. 

만약 – in case, if 

(만약) 지금 자면 – if sleep now 
(만약) 내일 밤에 비가 오면 – if it rains tomorrow night. 
내일 비가 오면, 집에 있을 거예요 – If it rains tomorrow, I’m going to be at home. 
이거 다 먹으면, 배가 아플 거예요 – If you eat all of it, your stomach will hurt. 
리모콘을 찾으면, TV를 볼 수 있어요 – If you find the remote control, you can watch TV. 
TTMIK에서 공부하면, 재미있어요 – If you study at TTMIK, it’s fun. 
지금 안 오면, 후회할 거예요 – If you don’t come now, you will regret it. 

if 

 action verbs ~ㄴ/는다면, ~았/었다면 

네가 안 먹는다면 배고플 것 같아 = If you don’t eat, you will probably be hungry
(만약) 공부한다면 성공할 거야 = If you study, you will succeed
(만약) 학교에 간다면 나에게 알려주세요 = If you go to school, let me know

descriptive verbs ~다면

제가 행복하다면 일을 더 잘 할 거에요 = If I am happy, I will work harder
제가 슬프다면 친구를 만나지 않을 거에요 = If I am sad, I’m not going to meet my friend

nouns ~(이)라면

만약 제가 의사라면 돈을 많이 벌 것 같아요 = If I were a doctor, I would earn a lot of money
만약 제가 선생님이라면 학생들에게 존경을 받고 싶을 거에요 = If I were a teacher, I would want to be respected by students

~았/었더라면 – if i ___, i would have.. regrettable past tense

돈을 다 쓰지 않았더라면 그 것을 샀을 거야 = If I didn’t spend all my money, I would have bought that
내가 사과를 다 안 먹었다면 너에게 한 개를 줬을 것이다 = If I didn’t eat all of my apples, I would have given you one
내가 공부했더라면 시험을 합격했을 것이다 = If I studied, I would have passed the test

~았/었/했을 것이다 – would have

내가 밥을 먹었다면 배고프지 않았을 것이다 = If I ate, I wouldn’t have been hungry
친구를 만났으면 재미있었을 것이다 = If I met my friend, it would have been fun