It expresses the reason or cause for something. Commonly used to explain the reason for one’s actions or to express to provide justification for something.
It expresses the discovery of a fact or situation. The first clause is the action and the second clause is about the discovery. This form can only be used with action verbs.
Example
아침에회사에가니까아무도없었어요.
When I went to the office in the morning, no one was there.
어제백화점에가니까세일을하고있었어요.
When I went to the department store yesterday, they were having a sale.