multiple template use

How do I create various documents, within one project, that use different templates?

Have you gone over the section on Document Templates in the interactive tutorial, yet? That’s going to be the simplest introduction to the feature. It is of course also documented fully in the user manual PDF, starting on pg. 72, §8.5 Document Templates.

Once you have a template folder set up, you should see them show up as options for creating new documents in the Project/New From Template/ sub-menu.