Microsoft released an update to the OneNote app in the Windows Store today. It introduces Pen and ink improvements, Support for Office 365 notebooks and offers a few fixes.
Pen customization while drawing and handwriting is now available, as well as the ability to quickly flip between customized pens. A radial menu will appear when a stylus hovers over the screen, providing a quick way to customize and switch between pens.
The OneNote app can access your notebooks on SkyDrive but with today's update, OneNote can access your notebooks on Office 365.
You don't need Office 2013 for using OneNote app. It's available for free on Windows Store.