What is the purpose of a footnote?

Footnotes are often used to display information about pages themselves such as the page number, total pages, or the source if printed. Some computer applications will automatically add this information whether it is wanted or not.
Footnotes are a way to collect citations and references at the bottom of the page rather than parenthetical references, which appear in the text itself. An even better way is to use end notes, which take the references to the end of the document, which clears up space if you have several references in one spot. For example, one paragraph can become closer to two in size with parenthetical references, and with enough references in footnotes, large portions of the page are devoted to that. Be forewarned; however, about what format you are writing in. MLA uses footnotes or end notes, but proper APA format requires the use of parenthetical references.