Click the + or - button to add a control point. The mouse button changes indicating that you can place a control point on your photo.

Clicking the + control point button automatically sets the Base File slider to 0%, making it possible to add the current filter effect only to the area selected by the control point, and places a control point with the Opacity slider set to 100%.

Clicking the – control point button leaves the Base File slider at its current value and places a control point with the Opacity slider set to 0%, removing the filter effect from the selected area.

Each Control Point has two sliders:

Size Slider
The Size slider affects the reach of the control point.  By increasing this slider, you can affect the objects similar to the object that the control point has been placed upon but are farther away from the control point.  When set to 100% the control point no longer bases its effect on the location of objects within your photo, instead relying solely upon the color, tonality and texture of the objects to determine whether or not to affect them.  Decreasing this slider will make the control point affect only similar objects closer to the control point.

Opacity
The Opacity slider controls to what degree the current filter effect should be applied to the selected area. A value of 100% ensures that the current filter effect will be fully applied to the selected area. A value of 0% prevents the current filter effect from being applied to the selected area.

The + and – options for adding a control point set the starting position of the Opacity slider, however the Opacity slider can be adjusted after the control point is added.