@55Yr-Comback
I hope that video answered the questions that you actually asked. But wait--there's more.
In Charlie's demo, he has his jaw set so that his upper and lower teeth are aligned. He also has the mouthpiece centered vertically (50-50) on his lips. That's a good place to start, but it might not work for you.
Some folks play with overbite or (less likely) underbite. Some play 50-50, while others use higher mouthpiece placement or lower placement. Some even offset horizontally. A lot has to do with your oral and dental structure. There's really no right or wrong if it works for you so, unless you have an instructor, you just have to experiment.
Sometime in the future, you may find this website interesting:
https://wilktone.com/?page_id=5619
From that site:
*Where no obvious reason seems to exist for the adoption of any particular method, it is in order to ask “Why?”.
And if the “experts” provide you too readily with an answer, bear in mind that they may not, in fact, have any clearer understanding of how successfully to perform the task than you do yourself.*