When you want to add some content or features to a card that isn't pure text, the place to go is the Universal Coupler, which can be accessed while editing a card by pressing the default shortcut (/) or by clicking the "+" button in the top right corner of a card in edit mode.
Once the Universal Coupler is open, you are given a number of options to choose from, which are:
Tag – Add one or more tags to a card
Parent – Add one or more parents to a card
Link – Add an internal bi-directional link (i.e. link to another Supernotes card)
Image – Upload an image
Icon – Add an icon to the card
Template – Create or insert a template
Emoji – Insert an emoji into the card
Color – Change the color of the card
Modifying the Coupler Key
There is an option to customize and record a new "Coupler Key" shortcut in the User Preferences.
Typing the Coupler's Shortcut as Text
Sometimes you just want to type a forward (or backward) slash. In those cases, you have two options:
Press ESC – this will close the Coupler and insert any text you typed into it (including the shortcut)
Press SPACE – this will close the coupler and insert the shortcut + a space.