The surplus occurs when your projected revenues exceed your projected spending, and it automatically goes to pay down debt.
How much debt should one aim at paying down? The answer is that it depends on where you are in the business cycle. When you have unexpectedly strong revenues, you should aim to use that to pay down debt. In years when revenues are weak, you would not be paying down as much debt. Indeed, it could well be that for one or two years you actually run a deficit, even though you're on track over time to bring it down.
All we've said is that it's really important over the remainder of this decade, given the demographics of this country, to aim to reduce the burden of the debt, both for the federal government and the provinces.