Rainforest: Place it on top of your substrate to:     

• Increase humidity in your enclosure
• provide safe cover for your clean up crew
• provide a soft layer for your critter to lay on. 

Forest Floor: place on top of your substrate or mix some in to:

• create a place for your detritivore insects to stay hydrated, you can do this by misting regurally.

Grassland: your can help add pockets of humidity to your setup by:

• placing Spagnim moss at the base of plants
• burrow a handful under the substrate for your clean up crew to stay hydrated

Desert:You can provide added humidity by:

• burrowing a few handfuls under the substrate to keep your clean up crew hydrated