Office Online is Microsoft's Chrome extension which allows users to create, edit and view Office documents from inside the browser.
The package gives access to Word, Excel, PowerPoint, OneNote and Sway Online without needing any other local software.
There's nothing too surprising here. You get access to local or OneDrive files, so it's not a convenient viewer for documents you happen to find online. And it's really only a wrapper for the existing Office apps, which don't offer much in the way of editing abilities.
Still, if you're already using OneDrive to host Office documents then Office Online gives you an easy way to work on them from anywhere.
Easily view and work on your OneDrive-hosted Office documents.