The background layer is reserved for the page template of your choice. This could be something preloaded, like a grid, or could be something that you imported from an outside platform. You can toggle the visibility of this layer on or off as needed.
To set a new background layer (or remove it), just tap on the background layer itself in the layers list. It will automatically bring up the background layer selection screen.
Adding a new layer is easy, just click the layer menu and then the little plus icon ("+"). You can add up to four of these layers above the background layer. If you have more than one layer, you can move them forward or back easily with the arrow icons, and you can toggle visibility as well.
As of this writing, Supernote does not yet support locking or grouping of sections of a layer. That means that if you are designing an apartment, and you place an armchair and a desk in one layer close together, when you draw a selection box around one part or all of the other may be selected as well. I’d love to see grouping as a function in the future, but, for now, you can use the layer feature to enforce simple grouping.
For instance, you can place different types of furniture on different layers to ensure that you can select and move specific drawn objects without accidentally dragging along others as well.
The world of e-ink devices is vast and confusing, with dozens of models from dozens of manufacturers.