고나서 Grammar- Beginner

고나서 

Expresses the fishing of one behavior followed by the beginning of a subsequent behavior and thus corresponds to ‘do (something) after’,  ‘upon finishing’, or ‘and then' in English. Although in some cases -고 can be omitted without changing the meaning of the sentence, such as in 일을 하고 나서 쉬세요 and 일을 하고 쉬세요， the inclusion of -고 나서 instead of simply -고 helps clarify the fact that the first behavior has completely ended.

Example:

1.아침을 먹고 나서 신문을 봅니다. I read the newspaper after eating breakfast.

2. 텔레비전을 보고 나서 잡니다. I sleep after watching TV.

3.숙제를 하고 나서 쉽니다. I rest after finishing my work.

Because -고 나서 expresses temporal order, it can only be used with verbs Further, when the subjects of the first and second clauses are the same in sentences using the motion verbs 가다 (to go), 오다 (to com리， 들어가다 (to enter) 들어오다 (to exit), 나가다 (to leave), 나오다 (to emerge [from]), 올라가다 (to go up), and 내려가다 (to go down), and the verbs 일어나다 (to get stand up), 않다 (to sit), 눕다 (to lie down), and 만나다 (to meet) -아/어서 is used in place of -고 and-고 나서. 

- 나는 학교에 가고 나서 (나는) 공부해요. (x)
- 나는 학교에 가서 (나는) 공부해요. (0)
    I go to school and (I) study.

**(나는) 오늘 버스에서 앉고 나서 (나는) 왔어요. (x)
→ (나는) 오늘 버스에서 앉아서 (나는) 왔어요. (0)
    Today, (I) rode on the bus and (I) came (here).