One of the things that I had to learn very indirectly was how to set certain shaders to figures/props/etc. For example, there's a great freebie called Cloth FX (I don't recall where I found it at the moment but Google will get you there) that you can use to set clothing items (or any surface, really) as either a leather effect or spandex. In order to do that, however, you first have to select the figure it's going on in your scene tab, then swing over to the surface tab and highlight what surface material you are going to use that shader on.

Now for the hidden part: Holding down control, click on the shader thumbnail in your file list/tree, and a pop-up box comes up. There's two selectable drop down options. The Top box has 'Surfaces' with the option Selected or All. (in this instance, we only want one or a few surfaces of your chosen item with the shader, so 'Selected' is clicked.)

The other box is 'Map Settings'. This is how it will work with the texture map or UV map of the item. The options are 'Replace' or 'Ignore'. Again, this time one would use 'ignore' which the shader with go over top of the texture map beneath, creating something of a dual layer image.

The control part and clicking on the thumbnail to activated it was the important part of all of this.

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