Dlady, don't you just love the obscure? Don't despair - it's the norm for me to look at new concepts with a big question mark over my head until I can figure away to understand them on my terms.
My take on it would be that it may help to think of it in terms of focusing ahead or riding towards a goal rather than 'using energy'. You're going to still use your physical aids of weight, hands and legs but your concentration is no longer directed at getting the horse to move for the sake of getting it to move but more at getting to a specific location in a specific gate (say down to the end of ring going from walk to trot part way there or going over a trotting pole, etc). Once you look at it that way, you'll probably find yourself seeing that the use of the aids becomes more second nature to you.
If you are sitting in a chair, all relaxed, maybe even slumped a bit, and you decide you are going to get up and go to the cupboard for a snack , first , you'll look up at the cupboard, you'll probably take in a bigger breath, kind of lift up your shoulders in anticipation, become a little bit lighter on the chair, lean slightly forward and stand up and move toward your goal.
It's that lift in your breath, your eyes, you spine and your weight, and your focus on the goal that is the rise in your energy.