Handset Designer references left and right when referring to one side or another of a Wall. These locations are relative to the direction the Wall is drawn. Once you highlight a Wall and see the direction, left is always the side on which the numerical length and the direction arrow appear.
Handset Designer offers several ways of identifying the orientation of the shapes you draw. Knowing Wall orientation is critical, because the left and right views of a Wall may differ, for example in a sloped floor. Most shapes (Walls, Curved Walls, etc) have start and end points. The direction of a shape can be determined in several ways. For example, when you highlight a wall you will see a numerical length with a grey arrow indicating the direction.