WordPress.org

1. Unpack the *.zip file and extract the /born-on-this-day/ folder and the files.
2. Using an FTP program, upload the full /born-on-this-day/ folder to your WordPress plugins directory (Example: /wp-content/plugins).
3. Go to Plugins > Installed and activate the plugin.

To add the widget: Go to Appearance > Widgets, add the widget to the sidebar of your choice and save.

To use the shortcode: Simply add [born-on-this-day] to your posts or your pages.