Acadia -

You know what a bump-map is, right?

A displacement map is similar, but takes advantage of the Firefly renderer's improved abilities, and gives much more realistic grooves, bulges, etc on the mesh.

Find a model in your Runtime that uses a bump map. Go to the material room, disconnect the map from the "bump" channel and plug it into "displacement".  You'll need to tick "Use displacement maps" in the Firefly render settings.

Experiment with a few different renders of your model, increasing and decreasing the displacement amount.

Tip - in Render Settings, ensure that "displacement bounds" is set to a higher amount than the setting you use in the materials room. This will avoid artifacts showing up in the render.