How do I add Customer Portal for my organization?
Customer Portal is automatically enabled if you add Portal Users.
To add portal users: Goto Setup > Customer Portal Settings > Customer Portal User > Add Portal User. Also, you can add a contact as portal user. Just open an added contact and click Add Portal User.
Now, customize your customer portal home page. Goto Setup > Customer Portal Settings > Customer Home Page> Add sections and widgets as per requirement.
For more details refer Customer Portal