Often we do things in sequential order and we want to tell others of what we do and in what sequence we did those things. All languages have many ways to express that, Korean is no different. The Korean time expressions -고 나서 is one of the forms you can use to achieve it.
The Korean time expression -고 나서 is simple to understand. With the form, you express you finished one action and perform another action after it. Therefore, this form is a rather simple way to indicate the sequence of actions. Because it puts actions in a sequence, you only use it with verbs.
In certain cases, you can drop the 나서 part from 고 나서, leaving only -고. Doing this changes little to the meaning in the sentence. We mentioned this earlier in our -고 article, where we told the form can also express a sequence of action. However, even though it changes little to the meaning in the sentence, there is an important difference to keep in mind. The form -고 나서 makes clear the first action is completely over before you started the second action. This is not made as clear when you drop the 나서 part.
가: 매일 아침에 밥을 먹고 나서 신문을 읽어요.
나: 정말? 아침에 저는 신문을 읽을 시간이 없어요.
A: I read the newspaper every morning after eating.
B: Really? I don’t have time to read newspapers in the morning.
How To Use
The grammar of -고 나서 is not difficult at all since it simply uses the same rules as those you need to know for -고. You simply need to take the verb stem and attach the form behind it. There is little else to it. However, keep in mind that this form can only be used with verbs, not with adjectives, nor with nouns.
Also, do not confuse -고 나서 and the form -아/어서 to express a sequence of actions. They have different uses. The first expresses you finished one action and after it started doing something else. However, the latter expresses you performed one action in order to do another action.