The "Clipping Box" function is located in the toolbar. The function can only be executed if  "Clipping Box" item is activated (right menu → forms).

Add "Clipping Box" Item

One of the main uses of the "Clipping Box" is the extraction of some of the points of a point cloud. Only the points inside the "Clipping Box" are displayed.

Place the Clipping Box element → Activate the Clipping Box element → Click on the "Clipping Box" function in the toolbar

The Clipping Box can be moved via the menu Edit --> Coordinates.