When you create a Cloud you have the option to set up sharing for the archives in that Cloud. By default, Clouds are private, meaning you can only access them with your subscription. However, you may choose to make your Cloud Shared or Public and assign read, write or full access to other users with their email address or Amazon ID. A Public cloud is also visible to any other BigCloud subscriber - they can read, but not write, Archives in that Cloud.
When you share a Cloud, you also have the option to enable "Requester pays", so that other users will be responsible for paying for the bandwiidth they use downloading or uploading to the Cloud. As the owner, you will still be responsible for the storage costs.
You can change the sharing setup for a Cloud at any time by going to the Cloud list in the Preferences screen, and clicking the "Edit" button. You can also reach the sharing controls from the Backup configuration of an Archive, when you click "Change Backup Location" with BigCloud Archives Online selected, you can also select a Cloud and press "Edit".