The red-framed area is the layers panel.
Here, you can manage everything related to layers.

You can show or hide the layers panel by tapping the icon at the top right.

Add layers
Clear the contents of a layer
Delete layers
Rearrange layers

Add layers

To add a new layer, tap the icon at the bottom left of the layers panel.

Clear the contents of a layer

1. Tap the layer you want to clear.
2. In the popover, tap Clear. This will remove everything drawn on the selected layer.

Delete layers

1. Tap the layer you want to delete.
2. In the popover, tap Delete. This will delete the selected layer.

Rearrange layers

To rearrange layers, tap and hold the layer you want to move and slide it up or down to its new position.