We’ve installed a plugin called “FD Footnotes” that will allow WordPress users to include footnotes in their posts and pages. To use the plugin, administrators need to first activate the plugin. To activate a plugin: login to your site, click “Plugins,” scroll through the list until you find “FD Footnotes,” click “Activate.” The plugin should now turn bracketed text into footnotes (see instructions below).
The following directions for adding footnotes to a post or page come directly from the plugin author.
Adding footnotes to a post is simple. Just type them inline in your post in square brackets like this:
Each footnote must have a number followed by a period and a space and then the actual footnote. They don’t have to be unique but it is recommended. It doesn’t matter what the numbers are since the footnotes will be automatically renumbered when the post is displayed.
For example, this:
Footnotes can contain anything you’d like (except square brackets) including links, images, etc. Footnotes are automatically linked back to the spot in the text where the note was made.
Note: Do not include square brackets  inside the footnotes themselves.
Note: Footnote numbers don’t need to be unique but it is recommended, especially if the text is identical for multiple footnotes. If you have multiple footnotes with the exact same text and number then you’ll get weird and incorrect footnotes on your post.