TOPIC: "of" and "For"

I have a problem concerning the usage of the "of" and "for". Sometime, I feel concfusing in using it. For example, is it correct to say "The manager of department A" or "The manager for department ."

Please help.
Thank you very much.

You would say " The manager of Department A...'
There are very few rules about the use fo prepositions. Try to become familiar with the collocations e.g. noun+prep, prep+adj., verb+prep, that you commonly use in your writing. The best way, in general , to familiarise yourself with prepositional usage is through extensive reading