Range markers are essentially two location markers the are grouped together to mark the beginning and end of a section in the timeline.
To create a new range, right-click on the Ranges ruler at the top of the timeline, then select New Range. Two markers with the same name will appear along the ruler. Both marks can be moved along the timeline by clicking and dragging them to the desired location.
It is also possible to create range markers from a selected range or region in the Editor window, or to use the Ranges & Marks List in the Editor list.