The Namespaces Tab lists all the Templates and Variables that have been made in this lesson. Once a template is made, it will automatically show under this tab. Once a template is in this tab, it can be dragged into the Storyboarder to build your scenario more efficiently.
It can also be used to create different Namespaces that can hold templates and variables that can be used across all lessons within a project.
For more information on Namespaces, see its section in the Templates Documentation.