Even though no viewer or camera exists yet we need a way of telling Blitz which side of the triangle will be visible.
The order clockwise/anticlockwise of the vertices is important because the order changes depending on whether you are looking at the front or back of the triangle.
You decide which is the front by imagining yourself standing in front of the triangle and the telling Blitz the vertices in a clockwise order 'From your imaginary viewpoint'.
Do it right and when the camera is created and placed at the position you were imagining then it will see the triangle too and the triangle will be drawn on the screen.
The order clockwise/anticlockwise of the vertices is important because the order changes depending on whether you are looking at the front or back of the triangle.
You decide which is the front by imagining yourself standing in front of the triangle and the telling Blitz the vertices in a clockwise order 'From your imaginary viewpoint'.
Do it right and when the camera is created and placed at the position you were imagining then it will see the triangle too and the triangle will be drawn on the screen.