Both DVDs, the "Black Diamond Railway" parts I and II show step by step how to apply ballast and ground cover and are the best way to learn how to apply these ground covers.  If a picture speaks a thousand words, a video must be a lot more!  However, the following bullets summarize these procedures.

Note that both Coarse and Fine Gray Mix should be used together for best results.

Applying Coarse and Fine Gray Mix:

• As an optional first step, you can use black paint to color the surface where you are applying the ground covers to.   This will hide any missed areas and keep the light colored plywood from coming through if the ground covers get rubbed off.
  

• Us the shaker to randomly apply the Coarse Gray Mix first. You can apply it in may different way.  As a suggestion, apply to a small percentage of the area you want to cover (~20%).  The bottom line is to make it look good and natural looking. 
  

• You can use a clean dry paint brush to move it around until it looks good.
  

• After the Coarse Gray Mix is applied, you then apply the Fine Gray Mix over the top.  Apply just enough to cover the surface without burying the Coarse Gray Mix completely.  It is ideal to blend them together.  Sprinkle the Fine Mix on lightly and uniformly to avoid having to use the brush to move.  Once you begin using the brush, it will not look as natural.  So hold the shaker at a higher distance and shake on small amounts at a time.
  

• If needed, you can use the brush to lightly pat down some areas to make adjustment.  Again minimize this to avoid making it look unatural.  Sprinkling it gives it a natural erroded or weathered look.
  

• Once the Coarse and Fine ballast are in place, thoroughly soak everything with undiluted scenic cement.  If you dilute by half, it will be half as strong once the glue dries.  Don't worry about the white glue, the glue dries clear and you will not notice anything.
  

• After the glue dries it is time to add static grass like you see in the photos.  Right after the glue dries and the surface is clean, is the best time to apply Woodland Scenics hobbytac glue.  You dab this glue in the areas you want grass, then lightly drop large amounts of Scenic Express static grass to the glue.  Overapply and do not press down.  Next use a small vacuum to suck up the excess static grass.  All that will remain is the grass in contact with the glue.  Since it was not pressed down, the vacuum should stand up most of the grass.  
  

• Now that the grass is applied you can add loose accents using fine black ballast, some Fine Gray Mix, and some Woodland Scenics grasses.