"i'm sorry : 죄송합니다 or 미안합니다 (Choi song ham ni da, or Mi an ham ni da.) i don't understand. : 이해를 못합니다. (E hae ruel mot ham ni da) have a good day!

i don't understand <---this phrase could also mean "잘 모르겠네요" if you don't understand what someone is saying, u can use this phrase. it contains a case when you really don't know the meaning and you don't know something because it is quite hard to understand.

i'm sorry : 미안합니다(mi an hab ni da) "i;don't understand: 나는 이해를 못합니다. (na neun E hae ruel mot hab ni da) bye~