i.RIDE_H0ndA

I hope it's OK asking questions as I go on this thread because I'm gonna have a few. I'm now working on the ailerons and I'm confused. In the image, the arrow pointing to the left that the words "Cut on this line", to which line is this reeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeerrrrrrrrrrr rrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrrre referring? I see dotted lines on the plans for the ailerons also but the line locations don't make sense to me. I cannot figure out where to cut.