~(기)만 하다 (~(gi)-man ha-da) – only does this (and nothing else)
This is an express you would use to say that a person or any other living thing only does a certain action or thing.
Omit the 기 particle if it’s a noun.
Example: 그 사람은 아무 것도 할 수 없고 찬소리만 해.
That person doesn’t know how to do anything and only make noise.
Add the 기 particle in front if it’s an action verb.
Example: 나 외식을 좋아하지 않으니까 집에서 요리하기만 해.
I do not like eating out so I only cook at home.