You just have to feed your points into that method and draw the result, i.e. if you want to draw a line between (10,10,10) and (20,30,50) use the method on both of them and draw a line (in 2D using Java2D's line method) between the resulting points.
But keep in mind that it can't look like it does in your example, because you are using parallel projection there but jPCT does perspective projection.