Each layer in a compound structure is typically displayed with some type of material. For example, one layer might be the air infiltration barrier, another is plywood, followed by a layer of wood. Revit has several predefined materials, or you can create your own using the Materials tool. See Materials.
The material on layers displays with fill patterns. To see the fill pattern in a coarse-scale view, set the Coarse Scale Fill Pattern and Coarse Scale Fill Color properties of the compound structure. To see the fill pattern in a medium or fine detail level, change the Detail Level parameter of the View Properties to medium or fine. See View Properties.