Translation
Also, when I have beaten the thrust or crossed swords with the player, I can put my hand behind his right elbow and push strongly so that I will turn him around and leave him uncovered, and I can wound him after turning him like this.
Interpretation
The elbow push is Fiores most common technique. Here, you are going to use it straight from the crossing of the master play. It is technically very simple, but requires good timing to work properly.
Your two opportunities in the play are either after the swords have crossed but before your opponents foot has landed, or having made the master play, your opponent is moving their foot to do something else. Their foot needs to be off the ground and moving somewhere at the moment of the push for it to work.
Catch their elbow with your left hand, and lock your arm in place. Step through with your right foot and push with your left hip. It is the hip which makes the push. Shove the elbow across the body. Your opponent will land facing somewhere off to your right. How far they turn is entirely dependent on how well the push has caught them. this will give you a free strike, as demonstrated by the 15th scholar..