OneNote’s docking feature is really useful for when you are taking notes from other documents. It produces a narrow version of OneNote which stays put even when you change the document or programme that is open in the other pane. This means you can switch between browsers, documents and spreadsheets to take notes on, and have them visible while you take notes. This is how it looks.
The Dock to Desktop button is already located in the Quick Access Toolbar. Give it a second to work as it has to rearrange things on your desktop.
I added the Normal View button to the Quick Access Toolbar to make it easier to get back out of the docked view when I needed to. You do this through the Customise the Quick Access Toolbar > More commands option on the drop down that you can open at the very right of the Quick Access Toolbar.