Layers separate your visual into parts, and are primarily used to keep items from interfering with each other. An example of a template that might need layers would be in a Floor Plan, where the first story of a house could be on one layer, and the second story on an additional layer.
Add a layer to your visual by choosing New Layer from the Layers drop down menu in the Page tab.
Type the name of the new layer into the Name field, and select or deselect Visible and Clickable from the New Layer dialog box. Selecting Visible allows that layer to be seen when you are viewing a different layer in your visual. Similarly, selecting Clickable allows that layer to be edited (ex: moving items around) when you are viewing a different layer in your visual.
Manage your layers by choosing Define Layers from the Layers drop-down menu, then selecting from the options in the Define Layers dialog box.
After you've added and defined the necessary layers in your visual, begin working in them by selecting the layer tab below your Work Area.