the triangles behave in a non-intuitive way? If one could understand the logic behind the interface, it seems one would have the power to draw better.

And thanks for the many ideas.

Thanks for prompt reply; will try your suggestion.

Just trying to get the very basics. For practice I thought I would create a regular tetrahedron from equilateral triangles. Made one and some copies, then tried to join two ends of a side to two ends of a side so I could fold the rhombus in half and get into the third dimension. Was able to get the triangle moved and join two end points, but the joined object does not behave intuitively, and moving almost anything, including the second end point, leads to changes in length of the sides of both triangles rather than moving the second triangle (I had selected it before moving).

I recognize that the triangle is probably laid out in polar coordinates rather than cartesian, but what rule is it following? Is there anything written on how to get these rules? Or just avoid this weirdness?

Unclear what B and C refer to: the points adjacent to A on the ground? Is the solid resting on a triangular face? Another view would help clarify its shape.

Is one supposed to be able to carry out the indicated operations on the provided file? Perhaps add the result of the rotation.