In this menu you will be able to activate the "Classifier" by clicking . You can drag the classifier around with your mouse, it will move on the plan dictate by the view. You can choose between "Cubic" or "Spherical" shape, and then decide the "Size".
The "Size" will be the radius of "Spherical" and the lengh for "Cubic".
Select the class to send the points in with the drop box. Then press"C" to classify.