There are a few different particles and verb expressions matching the different uses of "for".

"Write 10 sentences for homework" can be translated as (오늘) 숙제로 10개의 문장을 쓰세요/써 오세요, or 숙제로 문장을 10개 써 오세요.

(으)로 can take the role of "for" in this in kind of usage.  써 오세요 means do the homework(쓰다) and bring it (오다) to the teacher for verification, short for 써서 가져오세요.

Another example:  네 생일 선물로 자전거 사 줄게 = I'll buy you a bicycle for your birthday.

The other major use of "for" would be in the sense of "for (the sake of) a person/thing", which translates to  -를 위해(서).

e.g:  I did it for your own sake = 나는 너 자신을 위해서 그렇게 한 거야.