그래서 

오늘은 비가왔어요 그래서 집에있었어요 – today it rained so I stayed at home. 

~아/어/여서

먹어서 – eat  만들어서 – make  해서 – do  와서 – come 

Reason + result  비가 오다 (it rains) + 못 가다  (can’t go) 

비가 와서 못 가요 – It rains, so I can’t go 
비가 와서 못 갔어요 – It rained, so I couldn’t go.  
오늘은 바빠서 영화를 못 봐요. – Today I’m busy, so I can’t watch the movie.  
만나서 반갑습니다 (/반가워요) – I met you, so I’m glad = It’s nice to meet you. 
바빠서 너랑 얘기할 수 없어요 – I’m busy so I can’t talk
서울에 와서 좋아요 – I came to Seoul and I’m glad. 
술을 너누 많이 마셔서 머리가 아파요 – I drank too much so my head is aching. 
비가 와서 집에 있었어요 – It rained so I stayed at home.  
요즘에 바빠서 친구들을 못 만나요 – These days I’m busy so I can’t meet my friends
한국어가 너무 재미있어서 매일공부하고 있어요 – korean is so much fun that I’m studying it everyday.

An action + another action that takes place afterwards 공원에 가다 (to go to the park) + 책을 읽다 (to read a book) 

공원에 가서 책을 읽을 거예요 – I’m going to go to the park and read a book. 
친구를 만나서 밥을 먹었어요 – I met a friend and ate together.  
친구를 만나서 밥을 먹을 거예요 – I’m going to meet a friend and eat together.  

Action + purpose of or the plan after the action. 돈을 모으다 (to save up, to save money) + 뭐 하다 (to do what) 

돈을 모아서 뭐 할 거예요? – with the money you save what are you going to do? 
게익을 사서 침구한테 줄 거예요 – I’m going to buy a cake to give to a friend. 
한국에 가서 뭐 할 거예요? – After you go to Korea, what are you going to do? 
열심히 공부해서 장학금을 받을 거예요 – I’m going to study hard and/to get a scholarship

fixed expressions. 

-에 따라서 – according to 
예를 들어서 – for example 

계획에 따라서 진행하겠습니다 – I’ll proceed according to the plan. 
예를 들어서, 이렇게 할 수 있어요 – for example, you can do it like this.