If you need to add footnotes to your WordPress posts, then the simple Simple Footnotes plugin will do just fine.
With the Simple Footnotes plugin, authors can add footnotes to WordPress articles and pages with a simple shortcode. No additional parameters to the shortcode are required.
Plugins for WordPress [ref]The most popular CMS in the world[/ref] are rarely so simple and elegant.
The Simple Footnotes plugin independently counts the number of footnotes and their order. It displays the contents of all footnotes at the end of the article and places the corresponding links inside the article. Good markup allows site owners to change the look of the list with CSS, although the default styles will look good with most WordPress themes.
It is also worth noting that the footnotes themselves at the end of the article have links back to the places where they were placed inside the article, i.e. visitors will be able to continue reading from where they left off. In a recent update, the author added full support for multi-page posts and pages.
The presence of footnote text in the content of articles means that they will participate in site searches, unlike many analogs that write footnote text in metadata or options.
Simple Footnotes is written by lead developer Andrew Neisin, who believes WordPress plugins should be as simple as possible and do one thing well. With the help of this plugin, Neisin managed to demonstrate this.
The Simple Footnotes plugin can be downloaded from the official WordPress.org directory, or installed automatically by searching for “simple footnotes” under Plugins → Add in the WordPress admin panel.
If for some reason this plugin does not suit you, then there are several good alternatives, also from the official WordPress directory.