I think I understand now what you are saying about the citations. I'm sure you understand a lot of this already but I am going to simplify it so that I can try to explain it properly. If you have a sentence that looks like this:
The British fought the colonies in the Revolutionary War (Some book, Publisher 2010, S. 9).
Then the period goes after the parentheses because the book and page number refer to that specific sentence that you wrote. A direct quote would look like this:
George Washinton stated that "we will fight for our independence" (Some book, Publisher 2010, S. 9).
If you write an entire paragraph or several sentences that are supported by a citation, then it would look like this:
In the Revolutionary War, the colonies used a large number of local militia that were called minutemen. To coordinate these efforts, the Continental Congress established an official army and appointed George Washington as commander-in-chief. In fact, the Marine Corps considers its birthday to be in 1775. (Some book, Publisher 2010, S. 9-10)
Now, if I were to use the f or ff as you have, regardless of whether you are citing for a single sentence, a quote, or a paragraph, there will always be a period after the f or ff. This is because it is an abbreviation of the Latin word folio, and abbreviations always have periods directly after them. A good comparison would be "etc." It always has a period after it, whether it is in parentheses, in the middle of a sentence, or elsewhere. In researching online, however, I did find that there are a couple of fields in the U.S. that want you to never put a period after f or ff, but this seems to be an exception. If your instructors or other books in your field use a period after f or ff, then you should use it as well, in every situation.
Following these rules, this means there may be times when you have two periods very near each other, like this:
The British fought the colonies in the Revolutionary War (Some book, Publisher 2010, S. 9f.).
It looks silly but that's the way it is. Keep in mind that these are all rules I've learned in the U.S. and I have no idea if they might have different standards elsewhere. Hopefully I have at least cleared up some confusion though. And thank goodness my field uses footnotes, they are so much nicer looking.
