Sequence
This expression is used to indicate that first action completed before the subsequent action started.
Moreover, there is a before-and-after relationship between the actions in the preceding and following clauses.
This expression can only be used with verbs.
1. This expression cannot be used with the tense-indicating expressions -았/었- or -겠.
2. Both the phrases -고 and -고 나서 can be used to indicate the order of events.
When the first action get completed before the subsequent action started and there is a relationship between the two actions.