Create solid geometry with the Create Form tool.
 Draw panel, select one of the drawing tools.
Draw panel, select one of the drawing tools.  Form panel
Form panel
 (Create Form). A solid form extrusion is created.
 (Create Form). A solid form extrusion is created. 
 Form panel
Form panel
 (Void Form) to convert this solid to a void.
 (Void Form) to convert this solid to a void. You can change the dimension of an extrusion by using the 3D drag controls or editing the temporary dimension in the drawing area.