you can find instructions on how to add new templates to your document here:
Let me know if this helps.
I know we already talk about this, but i think making new template should be also at the context menu (right mouse click) at the nav. pane. :) I'm not using ribbon, almost never.
I have to disagree here. In my opinion adding new templates is not as frequent as using the templates or the other action commands. Our telemetry data backs this up as well. As I said, I'm hesitant to put just everything in here. I will move your question to the Ideas forum and mark this as "Not taken" for the time being. If many users are interested in having this particular menu item in the context menu, I'm happy to reconsider.
Thanks for your understanding!
Put the add template menu in the context menu of the navigation panel.