Draw Vs. Construct
In dynamic geometry technology, there is a distinction between figures that have been "drawn" vs. "constructed."
When you DRAW a figure, it may appear to be the shape you intend, but when a vertex is dragged, it no longer has the properties of that shape.
When you CONSTRUCT a figure, you use construction tools such as perpendiculars, parallels, bisectors, etc. to guarantee that the shape has the intended properties. When a vertex is dragged, the figure maintains its properties, and allows you to explore its geometric features and consequences. (Note that not all vertices can be dragged, since their location might depend on the rest of the construction and not free to move independently.)
Try dragging a vertex of each figure below.