Above the list of layers there is an icon of a blank page with a folded corner, clicking that will give you a new layer.On each layer there is an image of an eye, clicking the icon will toggle the visibility of the layer.They allow you to change parts of an artwork without touching the rest and change how things overlap in your artwork. On the side of your window, there should be a large grey box with a small purple box inside it that says 'Layer 1.' Layers are like painting on sheets of glass and placing the sheets on top of each other to make a picture.
