A collection of videos on how to do it. These videos are CONTRADICTORY. Open the throat vs close the throat. Keep the chin and jaw stable vs move the jaw. Various teachers are trying to verbalize what they do. What we hear may not be what they intend to describe. Or what they actually do may be different from person to person (though all their approaches are successful). For those of us older folks working without a teacher, perhaps just explore the exercises to find what works best for us.
This is a playlist of several videos. use the menu in the upper right of the video for navigation. So far my fav is the Robin Seletsky video. Also the Park House Creations one for the historic info.