As I achieve minimum competence, by my standards, with a little help from my friends, in aspects of making recordings, I directed attention to a neglected area, the voice, and devoted much of the fall and winter to scouring the fertile ground of YouTube for instructional videos on voice.
I identified five areas of study, the outline of which might save self-directed learners some effort and speed the process. They are:
I. Voice Maintenance
(a) Anatomy information. (See: Dr.Dan)
(b) Health and Wellness common sense.
II. Registers and Range
(a) Understanding Range
https://www.becomesingers.com/vocal-range/vocal-range-chart
(b) Recognizing and using Registers
III. Breathing technique (very important)
IV. Rhythm and Elocution -- consonants can be a challenge
V. Using the Snark (or other) tuner to practice pitch.
VI. Substituting harmonics for notes out of range, e.g.
if the low G is out of range, substitute B or D.
I am posting this list as a study guide. Any feedback appreciated. My method was hit/miss/stumble upon.

Ed, I like your link for determining vocal ranges. As an instrumentalist, I tend to write melodies that some vocalists find to be too large a range, and it's helpful to refresh this knowledge periodically.

Absolutely right about that, Matt, from my perspective. To further muddy the waters, naming conventions are far from it. Once, middle C was the C3 octave. Now the American Scientific seems to be winning, and it is C4. Steeped as I am in hymns, I am constantly reminded of how music has been written for choirs, which cover a wide range, although I rarely use the original score, but instead, lead sheets.
In the Key of C, in the octave C4, it is rare to see a tune drop more than two and one half steps below the first degree, meaning to a G note. Looking over my song book, it is not uncommon to see tunes with a range of seven or eight notes, occasionally breaking out above that practice for the sake of hearing the soprano. With choirs, I notice the basses tend not to draw attention to themselves. Here's another good one I came across:
https://www.liveabout.com/pitch-notation-and-octave-naming-2701389