The tutorial is for making a road or track through a forest.  In Photoshop, your create three jpg images which are then used as alpha maps (I think that's the term) to determine where certain materials appear. For example -- you apply a grassy texture to the whole terrain and then use the alpha map to tell it where the sandy texture for the tracks should go.

On the transparancy tab in my Infinite PLE, next to the Global transparency slider, there's a "drive with function" icon, when you click on it, you can tell it which alpha map to use.

The "drive with function" icon isn't there in Esprit so it looks like you can't do that in Esprit.