Get back to where you started from.
Long-press any button on the right side of your Pebble watch to set the target (current) location.
After you have set the target location, the app will wait for location updates from the phone. If you are not moving or your phone is not registering your movement, nothing happens in the Watch App. (Especially indoors the location of the phone will often not update at all.)
After you have moved away from the target location, the ring should show you the compass direction you should head to in order to get back. The numbers should show distance (in meters or kilometers).
Because Pebble doesn't (yet?) provide access to magnetometer, the GetBack watch app cannot show you true direction. You can only see e.g. "I should head southeast", not "I should correct my course a bit to the left".