During the 2018 Learn OneNote Conference, Marija Petreska shared a link to her amazing, free OneNote course for Teachers. This is the best I've seen. It is just too good to keep to myself.
I've used OneNote for many years and have come across a few tutorials/courses of OneNote but, I must say, this is the best I've seen. It is in the form of an online OneNote notebook, so you can quickly navigate to the section you are interested in. It is done in a highly visual form, with integrated video, when you need it.