What are layers and how do I use them?

The layers tool button can be found to the right of the spread in the toolbar.

Layers separate transparent levels of content rearranged in order from front to back. Content on individual layers can be hidden, merged or edited. By default, each spread opens with a single layer. Adding a background automatically creates a new layer to the back of the default layer.Layers - add multiple layers to your spread and edit backgrounds.