Sometimes you won't have time to think about where to put a particular note. For example, suppose you're in a meeting where you're discussing the week's activities with your colleagues. Suddenly, you have a thought about your stock portfolio, something completely unrelated to the meeting. Rather than disrupt the flow of the meeting to run OneNote, find the section containing your portfolio information and type a note to yourself, you can create a quick reminder note in your Unfiled Notes where you can follow up with it later. It's easy and there's only one step to remember, <Windows key + N>.
Unfiled Notes is a special area in OneNote where you can just throw a bunch of your stuff and then deal with it later. To create a new unfiled note, press the <Windows key + N>.
Then, After the meeting, when you have more time to organize your notes, you can click on the Unfiled Notes button in OneNote, found at the bottom-left of the NavBar.
This can be done in one of 3 ways:
Side note default options can be changed by simply right-clicking on the Side Note icon in the Windows System Tray -> selecting Options -> and then clicking on OneNote Icon Defaults.