How do I create case from Service Portal in Customer relation management module

[visha]

How do I create case from Service Portal in Customer relation management module, in the below picture I have highlighted with Red where I would like to insert a link or button to create a "case"  

[ian_cox]

Do you have an option to select a different CSM portal from the header drop down?

[ian_cox]

Here is how it is supposed to work Create a case from the customer portal

[visha]

That option Create Case itself isn't coming on portal. How and where do I configure to insert that link "Create Case" in portal.