Editing Nodes on a Geometrical Shape
There are multiple ways to modify an object in your drawing. If the object is a rectangle, an ellipse, a star or a spiral, i.e. a geometrical shape drawn with one of the shape tools, then this object is a shape, and not a path.
Shapes can only be modified by dragging their specific handles. In contrast to shapes, you will edit a path with tools that are meant for modifying paths.
However, shapes can be converted into paths, so the path tools can then be used with them.
To convert a shape into a path:
Select the shape with the Selector tool.
In the menu, select.
A shape can always be converted to a path, but a path can never be converted back into an object!