For example,don't aim at the platoon, don't aim at the British Soldier, don't aim at his chest, aim two inches to the right of the third button......breathe out......hold.....squeeze......and make every shot count.
I took it as a metaphor for concentrating on your goal and setting a high standard of performance.
Even if that isn't the correct interpretation of what was meant I thought it was a key moment in the story. The father only has a few seconds to give instructions to his youngest sons before sending them into the ambush to save their brother. He chooses to use this metaphor to tell his sons what he wants them to do. Both sons nod and you can tell they have complete understanding.