Five useful Korean expressions. 

1. 안녕하세요. This expression is a general greeting.
2. 감사합니다. It is a phrase used to express gratitude.
3. 죄송합니다. It means "I'm sorry" or "I apologize."
4. 도와주세요. This expression is a request for help.
5. 잘 모르겠습니다. It means "I'm not sure." or "I don't know well."