In May 2017 in an Education focused event Microsoft had announced Windows 10 S their new version of Windows 10. Windows 10 S allows installation of apps only through Windows 10 Store. Microsoft had then released the Store version of their Office apps on the first Windows 10 S device the Surface Laptop.
Recently, newer and cheaper Windows 10 S devices are available in the Microsoft Store. Also Microsoft had started delivering ISO files of Windows 10 S through the MSDN website for its subscribers.
Now that Windows 10 S has reached to different devices Microsoft has now enabled the downloading of their Microsoft Office Suite apps on any Windows 10 S device. Earlier only users of Surface Laptops were able to download these Office apps from the Windows Store.
Office Desktop apps that are available for users running Windows 10 S includes Word, Excel, PowerPoint, Outlook, Access, Publisher. Thses apps are 32 bit versions of the Office apps. While there is no OneNote app in this list but you can use the OneNote UWP app. Thses desktops app are Centennial app which means that are converted from the Win32 desktop apps using the Desktop Bridge program (project Centennial).
If you are running Windows 10 S you can go to Store and download them.