The applet helps observe the sections of a cylinder by a plane. Roughly speaking, the applet displays two objects: a cylinder and a plane that can be controlled with a mouse separately and also simultaneously depending on which of the "radio buttons" at the bottom of the applet is checked.

Objects can be rotated with the left button pressed or translated with the right button pressed. Pressing the left button while the Alt key is down lets one zoom in and away from an object. When the "combined" button is checked the cylinder will move as usual but also together with the plane.

The possible sections are circles, ellipses, and parallel lines that may coalesce.