How to create sample/demo templates?

There are two types of sample templates: 1. Regular/Calendar Note templates and 2. Meeting Note templates.

1. Regular/Calendar Note Templates

Right click (macOS) or long-press (iOS) "Templates" in the sidebar > "Create sample templates":

2. Meeting Note Templates

When you attempt to create a Meeting Note, you will find a button "Create sample templates" at the bottom in the menus on iOS and macOS. 

macOS: You create Meeting Notes by clicking the event in the right sidebar, then "Create New Note". 
iOS: Long-press the event at the top or tap on the event in the timeline (at the bottom) to open the menu, then tap on "Create New Note".