The Supernotes editor has a very simplistic templating system that allows you to easily save "templates" that can be then easily pasted into another card.
All interaction with the templating system currently happens via a submenu in the Universal Coupler, which as always can be opened with its shortcut (/ or \) or by clicking the "+" button in the top right of a card. Once the Universal Coupler has been opened, the Template Coupler has a shortcut for accessing it, which is just pressing the equals key (=). Or you can just navigate to the Template coupler with your arrow keys / mouse.
Once inside, you have two options:
create a new template by typing some text (this will be the template's title) and selecting the create new template button (green button with a plus at the top once you've typed any text). This creates a new template with whatever content was in the card when you created it.
select an existing template, which will be immediately injected into the content of your current card
And that's all there is to it with Templates! Currently only body text is supported to save as a template, but in a future update we plan to add more functionality to templates.