This stuff looks so good. I've downloaded the SketchUp software and after hours of trying, I can't get it to draw a straight line. I'll keep trying but I'm not holding my breath.
It made no sense to me but i was determined to finally get a grasp of it. Watched some youtube vids, when I encountered problems I googled it which typically brought me to the sketchup help site.
To me when I realized it was perspective it made more sense. Like if you wanted to draw a line up, look at it from the side rather then some weird skewed/cock-eyed perspective and it will snap to the axis you want. (b/g/r for xyz)