Plugins are used to extend functionality within WordPress.
They are often built by individuals or companies to allow integration with other sites or to add custom functionality or features to your site that isn’t required for the basic version of WordPress. Most users will only require a small amount of plugins on their site, if any.
You can find a comprehensive list of WordPress plugins in the “Plugin Directory“. You can also find them by searching within your admin under Plugins -> Add New.
Plugins can be installed via the plugin directory within your WordPress admin or you can download a zip of the theme and upload it via FTP to your wp-content/plugins folder on your web server. Once uploaded it can be found under ‘Plugins’ in your admin and activated.
You can see a list of plugins that FrogsThemes recommends.
More details on WordPress plugins can be found at “Managing Plugins“.