"Order" - This determines the number of Control Points on the spline. For example, selecting '3' means there will be 3 points on the spline that can be moved, as well as 3 points off the spline that will control the slope.
"Initial x-value" and "Initial y-value" - These values determine where the left most Control Point will be.
"Scale x" - This determines the right most location of the Control Points (on the spline). To figure out where this point will be, add 'Initial x-value' to 'Scale x'.
"Scale y" - This determines the distance (in the y-direction) between the Control Points on the spline, and the ones that control the slope.