The main idea of the Dashboard Templates - to save efforts on drawing similar dashboards for identical systems by defining one graphical template for similar dashboards and mapping rules to use specific registers for each dashboards.

So for descendant dashboards #1,#2,#3 (based on a template) their graphical representation is taken from template and the registers linked to their controls are taken from specific for each dashboard mapping list.

The dashboard templates are created like any other dashboard (if you have many templates and categories for them you may hide 'Templates' entry in the side bar menu) :

With the idication that it is a template:

In the dashboard list, the template column indicates type of a given dashboard - simple dashboard (empty), template, or based on template.

After you select some dashboard as a template for another dashboard, a mapping list will be provided to set connections or registers (right side) substituting original ones (left side) in the template.

TIP: If some dashboards are almost identical and differs only in some graphics, you can define visibilty 
registers for template and its descendants, so that substituting register value for a given dashboard has a bit 
mask to hide some elements and show others.