So, you have created a tab template and now you want to add it to a Card.
If you haven't set up your tab template, first see "How do I create a Tab Template?".
Create a new Tab using your Template
Click the "Add Content" 
button.
The "Add Content" dialog will open.
Name: Enter your new tab's name.
Template: If your Project has any tab templates set up, the template drop-down menu will display. Select the desired template.
Click "Add" to create your new tab.
Your new tab will be created.