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Download the 'arkayne-site-to-site-related-content.zip' file to 'wp-content/plugins/'.

Unzip the file using 'unzip arkayne-site-to-site-related-content.zip'.

You should now have: 'wp-content/plugins/arkayne-site-to-site-related-content/arkayne.php'.

Activate the Arkayne Plugin plugin using the Wordpress admin panel under Plugins tab.

Follow the click by click instructions for activating the widget to the right of the 'Activate' buttons.

Optional: Set WordPress specific display and caching options.