Before you can start using Commerce, you must purchase a subscription.
For information on how to do so, please contact an Oracle sales representative: http://www.oracle.com/us/corporate/contact/index.html
After purchasing your subscription, you will receive an email asking you to activate the service by confirming your order. An Oracle representative will then contact you to provide the URLs for your Commerce environments and the credentials you use to log into the administration interface and other parts of the site. You will also receive additional information with links to extensive resources to help you get started.