How do I add Customer Portal for my organization?

Customer Portal for your subscription would be automatically enabled when you add a portal user.

To add portal users to access your organization's self-service portal, follow the steps mentioned below:

Go to Setup>Customer Portal>Users
Click Add Portal User and provide your customer name and e-mail address
Click Create New Portal User, to send an invitation to your customer

Once your customer receives the invitation, they can create their login credentials and access your self-service portal.