You can install Footnotes via the plugin store, or through Composer.
To install Footnotes, navigate to the Plugin Store section of your Craft control panel, search for
Footnotes, and click the Try button.
You can also add the package to your project using Composer and the command line.
Open your terminal and go to your Craft project:
Then tell Composer to require the plugin, and Craft to install it:
composer require verbb/footnotes && php craft plugin/install footnotes