We put the thumb on the ridge that separates the silk notched portion, and uses the index placed on the back. The razor must be kept firmly!
We put the razor back flat on the leather and it grows from left to right in fleeing the edge.
Pressure must be constant, the number of passes is variable depending on the fineness of your initial sharp. But you know you're on the right track when it will be attracted by the leather and as far as the edge is refined.