Thank you! These are a great help. They showed me how to lay out a rectangle on the green-red axis, with the long dimension parallel to the green axis and the short dimension parallel to the red axis.
But then when I tried to rotate it (still in the green-red plane), only one of the four lines it was made up, rotated. The result was something that wasn’t a rectangle anymore.
Is there a way to tell SketchUp to freeze the rectangle in the size and shape it presently is, so that I can click on it and move the entire thing with one stroke of the mouse, instead of moving only one of its lines while the other three stay still?
And then how to rotate the whole thing (all four lines at one) to a new angle in the red-green plane? So that now none of the four sides are parallel with either the green axis or the red axis, but the rectangle is still the same size and shape as what it started?
Other thing I’d like to do is to “lift” the rectangle (that is, move it in a direction parallel to the blue axis) to make a 3-dimensional box. This would form a second rectangle, directly above the first and at the same angle.
To help me out with a shortcut(s), can anyone clue me in on what mouse/keystroke moves would accomplish that? Hopefully when I get those basics in my head, I can carry on from there and start figuring out more and more stuff.