To use box tool in modeler
Create > Box or press Shift (x)
If you would like to use the box tools in modeler, you must choose the Box option from the Create menu or just press Shift (x). In the modeler, there are several primitive shapes that you can use to create 3D model. In LightWave 6.5, primitive shape is the basic tool to create complex models, and it is also the basic element of 3D environment.
When you are satisfied with the image, deselect the primitive tool by clicking on it or choosing The Deselect tool under the Modes to turn your outline into an object (and alternatively, you can select another modifying tool.).