The Worm Gear lever position determines the direction that the tool will travel when turning or facing. "Down" position powers the apron from right to left, and "Up" drives the cross slide from front to back. I used those conventions as my default directions in the pictorial. Some others might choose to use left to right as their default convention on turning operations, in which case the Worm Gear lever would remain in the "Up" position for both turning and facing. The Gear Slide position transfers the drive setting between turning and facing operations.
I hope I understood the question correctly and this is helpful in explaining.
The only other lathe experience I have is with my first lathe, a Grizzley G4000 (9x20). So, I don't know how the N controls differ from other popular SB models. But, I found them a bit confusing when being away from it for a while, so the diagrams help me quickly refresh as a reference.
Thanks for the question.