Tethered digital camera operations mean's that the camera is connected to the computer
and remote operation such as set/get camera settings could be performed or
a capture is physical trigged on the camera and application is trigged to
download the captured image.
Darktable have now this feature (minimal but fully working) and are accessed thru the
device panel and the button "tethered shoot", if the button not is present under your
detected camera the camera has no support for it.