1. The instructions from this guide are referring to the WP Admin dashboard.
  2. You can get to this dashboard by adding /wp-admin to the end of your site’s url (e.g.: example.wordpress.com/wp-admin)
  3. Settings -> Webhook
  4. You can choose an action and the fields associated with that action to be posted to the URL.
  5. Possible Actions/Fields

via Webhooks — Support — WordPress.com