This article assumes you are using DAZ Studio 4.5 or higher. However, the basic principles are the same in all versions of Studio. A shader differs from a regular texture preset in Studio. A shader adds additional properties to the surface of the model. It can be combined with an existing .jpg texture or used alone.
When you apply a texture, you should have both the model and one or more surfaces selected. If you have only the model selected, but do not have an surfaces selected, the shader will not apply to the model. Model includes anything like a figure, hair, Genesis, Victoria, clothing, prop, building, and so forth in the scene that would appear in a render.
You can check to see what you have selected in the Scene Pane (WINDOW --> Panes --> Scene). The model you wish to apply the shader to should be selected.
You can select one or more surfaces of the model in the Surfaces (Color) Pane (WINDOW --> Panes --> Surfaces. With the model already selected, you can select the name of the model in the top left of the Surfaces Pane. Here you can expand the name so that all the surfaces (one or more) for the particular model are displayed. Select one or more surfaces.
Now you can apply the shader. If you wish the shader to be combined with the existing texture preset, you should hold down the Control (CTRL) button (Windows) or the Command (CMD) button (Mac) when you double-click the shader preset to apply. If you do this, you'll see a window called 'Shader Preset' appear.
In here, you can have 'Selected' for 'Surfaces' and 'Ignore' for 'Map Settings.' Then you'll get the shader applied to the surfaces you selected and keep the existing .jpg texture.
ELITE HUMAN SURFACE SHADER QUICK USE GUIDE