Once you have created a new shape, you can add it to the timeline like any other video overlay or PiP object. Once on the timeline, you can modify its size, shape, position, and orientation right in the preview window.
If you would like to perform more advanced edits, select the shape clip in the timeline and then click the Designer button to reenter the Shape Designer. When you have finished your edits, click the Save As button to save it as a new template or OK to apply the changes on the current template.