When a singer begins to sing, there is a word called “onset” that can be used to describe this beginning. This word causes me to think of a clinical static adjustment. I much prefer the term “launch” as it indicates dynamic energetic movement.
When we launch the tone, there is a breathing in and having this airflow immediately reversed to meet the cords in that split second when they close. Moving muscle and moving air syncing up at the exact same time, full of energy.
When this happens, we have a sensation and see with a mental imagination that we have caught the breath in and up; quickly launching that air in a downward laying movement on top of the step or pitch platform.
I imagine it is kind of like breathing up a little bit and then having my vocal “airplane” ride that air along a level surface with energy lifting the wings till I soar. This is difficult to explain in words, and makes more sense if demonstrated with the voice as well as an exterior physical hand motion indicating a loosely analogous internal feel.