Blending, vowel formation, breathing, articulations, and many other techniques cannot be taught the same way a stringed or brass instrument is taught. A person's individual vocal instrument doesn't have buttons or strings that can be pushed a certain way to produce particular sounds the same way every time. And each personal instrument can sound different.
Voice teachers and conductors may resort to telling some abstract visualizations to help. The vocal mechanism is basically a tube from the lungs to the mouth where the sound is controlled by the vocal folds in the larynx and modified by the tongue, teeth and mouth shapes to created tones and words. In order get the students to produce good breath and tone quality, he may use instructions like "breathe from your diaphragm," use a "sky hook" to maintain good posture, or "imagine focusing the tone from your raised soft palate", etc. They may never use the actual anatomical terms because most people don't remember difficult words like that.
Dr. Brent Wells who currently teaches choral music and directs two choirs at BYU, gave a lot of good advice today in our workshop. I appreciated how he wanted our choral group to learn to agree on vocabulary so that we could more easily adjust our tone production during rehearsals.
For example, he wanted us to learn five different positions to be able to produce our blended choral sounds. For instance, #1 would be a very bright, nasal sound. He demonstrated this by touching the tip of his nose and singing like "Ado Annie" from the musical "Oklahoma." That character's sound was not a good choral sound because it cannot easily blend with other voices. He had us try to replicate that sound. (Not pleasant.)
#5 sound is created by singing deep in the throat (or lowering the Adam's apple). This is too dark of a sound and not easily blended.

He worked with us to do a better job of pulling air into our lungs using the muscle of the diaphragm. (Incidentally, the diaphragm is a flat muscle like a pancake that only has one job -- to pull air into the lungs. It cannot help support the tone.) We worked on keeping our breastbones high and still, and supporting the tone with our abdominal wall muscles.
Getting a blended beautiful sound from a choir takes a lot of effort from everybody and it starts with having all the singers agree on choral vocabulary and how to use it.