Answer
If you quote another author (using his exact same words) or if you stipulate another author's theory, argumentation, idea or group of ideas, then a footnote must be used in order to clearly identify the source of your information.
Answer
A proper format could be:
Author's name, "Title of the essay", in Name of one of the book's authors et al., Title of the book, city where the book was published: publisher's name, year of publication,
Answer
There are two dimensions that we must consider in regard to your question:
1) the theoretical use of footnotes; and
2) the context in which such footnotes would be used.
Let's start with the use of footnotes
