When you are in Sectioning mode and you click Show 2D View, the 2D section window is displayed in a new view in the graphics area. Click this button again to remove the 2D section from the view.

You can perform the following operations in the 2D section view:

When you modify the section in the 2D view, it is simultaneously updated in the 3D view and vice versa. By default, the 2D view zooms in or out to fit the window. To view the 2D section at its original size, clear the Automatically fit 2D view to window option in the Model-Sectioning option in Global mode. Concurrently you can set the axis direction in the Up direction option of the Preset Sections in the Model-Sectioning option in Active View or Default mode to view the 2D view in the direction of your choice.