G'day, I'm not korean, just a student so I may be wrong, but my understanding is that we use 'for' when we translate from Korean to make it sound more natural. As a rule of thumb i feel 'for' can be expressed either: 을/를, 이/가, 위해, (~를 위해) 용.
"For our language exchange tomorrow let's talk about travel." - "내일 우리 언어 교환이 여행에 대해 이야기할까요. --- But this doesn't sound right -- "내일 우리 언어 교환이 있을 때 여행에 대해 이야기할 수 있나요? sounds better.
"for our meeting today, i want to...." -- 저는 우리의 희의가 하고 싶....."
"For studying a foreign language, speaking is very helpful." --> I don't think this sentence works in English :) you would probs say "when you study a foreign language, speaking is very helpful" would sound more natural.
위해 --> 엄마 위해 저녁식사를 만들었어요. -"For the sake of my mother, i made dinner"
용 (를 위해) --> 한국어 공부(를 위해)용 책 -- "A book for studying Korean"
를/을 --> (나는) 내 시험을 열심히 공부했어요. "I studied hard for my exam"
이/가 --> 시험이 열심히 공부하는 것이 어려워요. "Studying for an exam is hard"
And I usually use "ㄹ 때/ 때" (when) more often than "for" because i know that for doesn't really exist in Korean.
So hopefully this helps, But yeah I'm not a native Korean, just a student. SO if i have made any mistakes i apologise. If you have other q's about this or i haven't explained well enough, just tell me.