To apply a displacement you have to switch to the advanced sectioin of the material room. To add the displacement map, drag with your mouse from the little icon on the right side of the word Displacement, release the mouse button when it's on an empty part of the background, and choose New Node from the menu that pops up.
You'd best start with using image files for displacement maps, so choose 2D Textures ->Image map from the submenu. Now you can browse for the displacement map image file.

The number that appears instead of the question mark in the root node tells Poser how strong the maximum displacement effect should be. The number is in centimeters.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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