ISOMETRIC BASICS
 

Fig. 1a shows the X and Y axes in flat, 2-D orthographic space before being translated into an isometric view.

Fig. 1b shows the three isometric axes in an isometric view.  They are at 120 degrees to one another in 2-D space.  Another way to interpret the relationship of the axes is to say that the Z and X axis are 30 degrees from a horizontal plane. Take note of these various angles and as they will be used later in the tutorial.

Figs. 2, 3, and 4 show how orthographic shapes can be transformed into isometric planes (faces) laying parallel to the three isometric axes.