A footnote is a text element at the bottom of a page that provides additional information about a point made in the main text. The footnote might provide more information, offer an alternate viewpoint or list a citation for the source of a quote, idea or statistic. Endnotes serve the same purpose but are grouped together at the end of a chapter, article or book, rather than at the bottom of each page.
Figure 6.24. A footnote automatically postioned at the bottom of the text frame. A pre-made footnote style with a rule above is automatically applied to the footnote text.
Fraction-size superscript numbers must not introduce the footnotes themselves… [S]uperscript numbers don't make sense and are a disease… Since one should be able to find a footnote quickly, the normal number in the type size of the footnote must be used, never a superscript."
 Jan Tschichold: "Typesetting Superscript Numbers and Footnotes" in The Form of the Book, p. 124.
In CS2 you can create footnotes that are anchored to the location of the footnote reference number in the text. You can also import footnotes from Word or RTF documents. When the reference number moves to a new page, the associated footnote moves with it. To insert a footnote, place the insertion point where you want the footnote reference number to appear and choose Type > Insert Footnote. The footnote area expands as you type.
Choose Footnote Options to control the numbering style, appearance, and layout of footnotes.
Part I: Character Formats
Going with the Flow
Getting the Lead Out
Kern, Baby, Kern
Sweating the Small Stuff: Special Characters, White Space, and Glyphs
OpenType: The New Frontier in Font Technology
Part II: Paragraph Formats
Aligning Your Type
Paragraph Indents and Spacing
First Impressions: Creating Great Opening Paragraphs
Dont Fear the Hyphen
Mastering Tabs and Tables
Part III: Styles
Stylin with Paragraph and Character Styles
Part IV: Page Layout
Setting Up Your Document
Everything in Its Right Place: Using Grids
Text Wraps: The Good, the Bad, and the Ugly