The Region Selection group box provides various tools for changing where the effect is applied.
The Paint Region button will let you use the brush tools to draw-in and erase-out where the effect is applied.
The Select Region button will set the current selection as the area where effects are applied.
The Invert Region button will invert the mask. Regions that used to not have the effect applied will now have the effect applied, and vice versa.
The Reset Region button will make all pixels show the effect.
Select an effect from the drop down list to apply to the pixels within the region.
Alternatively, make a selection with the selection tools, then choose the effect. A Regional Effects layer will be created automatically using the effect you have chosen.
The following list of effects can be used with the Regional Effects layer: