Range markers are essentially two location markers that appear in the Range Markers ruler, and are grouped together to mark the beginning and end of a section on the timeline.

Creating a Range on the Timeline

There are multiple ways to create range markers:

Right-clicking on the Range Markers ruler at the top of the timeline, then selecting New Range.
Left-clicking and dragging right on the Range Markers ruler. This will render a red-filled area across all tracks and busses to help preview the extent of the range in creation. Once the mouse button is released, a paired range marker will be created.
Selecting a range in the Editor window, then right-clicking and selecting Add Range Markers.
Clicking New Range button at the bottom of the Ranges & Marks sidebar. The markers will be created around the playhead position, unless the playhead in at the time origin (in which case the markers will be placed at the time origin position).
Right-clicking a location or a CD marker and selecting Create Range to Next Marker. This will create a pair of range markers that start at the selected marked and end at the position of the next location or CD marker (both rulers are taken into account).

Editing a Range

Both markers of a range can be independently moved along the timeline by clicking and dragging them to the desired location. They can also be moved together by -dragging one of the markers.

Any pair or range markers, including session start/end markers, can be repositioned to the extents of an existing range selection on the timeline by right-clicking on either of the markers and selecting Set Range from Selection in the menu.

Renaming Range Markers

Ardour provides several ways to rename an existing pair of range markers:

Double-clicking either of the two range markers will show a dialog for setting a new caption for the markers.
The same can be achieved by right-clicking on either of the markers and selecting the Rename Range… menu item.
Additionally, the name can be edited in the Ranges & Marks sidebar.

Removing Range Markers

Range markers can be deleted in several ways:

By clicking on one of the markers and pressing the Del key.
By right-clicking on one of the markers and selecting Remove Range.
By clicking the markers' x button in the Ranges & Marks sidebar.

Additionally, all ranges can be removed at once by right-clicking on an empty part of the Range Markers ruler and selecting the Clear All Ranges menu item.

More Options

The context (right-click) menu for range markers has more options than the ones mentioned above:

Play Range	Starts playback at the left marker in the pair and stops at the right marker.
Locate to Marker	Moves the playhead to the selected marker.
Play from Marker	Moves the playhead to the selected marker and starts playback.
Loop Range	Creates a loop range off the selected range markers pair and starts playback.
Set Marker from Playhead	Changes the position of the selected marker to that of the playhead.
Zoom to Range	Changes the zoom so that the area defined by the range markers would be maximized yet visible entirely within Ardour's window.
Glue to Bars and Beats	When this option is enabled, the marker maintains its position in bars and beats even if there are changes in tempo and meter.
Loudness Assistant…	Launches the Loudness Assistant to analyze the selection defined by the selected pair of range markers.
Export Range…	Exports the selection defined by the selected pair of range markers.
Promote to Time Origin	This makes the position of the chosen range marker the origin time. This is mostly useful when the Display delta to origin marker clock mode is enabled to display the difference between current playhead position and the origin time. Absolute time stays unaffected.
Hide Range	This hides the range from the Range Markers ruler. Marker's visibility can be restored in the Ranges & Marks sidebar.
Separate Regions in Range	Cuts all regions crossing the positions of the range markers.
Select All in Range	Select entire regions that cross the borders of the range markers.
Select Range	Create a selection from the range markers in all selected tracks and busses.