Auxiliary clipping can be globally enabled by selecting it in the menu:
The Plane Tool will become visible and all objects on the negative Z side of the plane will be clipped (assuming the plane currently intersects some visible part). You can now manipulate the Plane Tool to achieve the desired display effect (see Use the Plane Tool for details).
Note: Auxiliary Clipping always uses the infinite extent of the plane specified by the Plane Tool - there is no way to restrict it to the rectangular bounds of the tool.
Each part has an attribute that controls whether it is clipped by the Auxiliary Clipping plane or not. To toggle this setting:
Select the desired part (see Select Parts).
Click the Auxiliary Clipping toggle.
(The Aux. Clip attribute can also be toggled in the Feature Panel for the part. See Set Attributes.)