Reference is a basic element that can emulate another element's look and behavior. Or say, it can work as an Element Reference.
You can find the "Reference" element in the elements pane, and add it into your page. It looks like:
That means it has no reference target yet. You can specify its target from the tools panel.
After specifying the target element, the Reference element will emulate the look of target element.
Since the Reference element is just a reference of the target element, resizing the Reference element will not affect the target element.