The 'Get Office' app is one of the apps that comes preinstalled with Windows 10. But it wasn't very useful for most users as it only showed information about Office 365 features. In the latest Windows Insider build, the app has got an update which Microsoft feels will be more useful. In current builds, the app's branding still remains "Get Office", but it is expected that Microsoft will rename it to "Office Hub".
The updated app will allow you to quickly open all of the recent Office files you've been working on and see information about your Office 365 subscription and manage it. You can also install new Office products from there, find help or request support from Microsoft.
It's worth noting that the new Get Office (Beta) app that is released to Insiders is a Project Centennial app, meaning it's a Win32 app with access to UWP-specific features like notifications, live tiles and more. That makes it a desktop-only app that won't work on your Windows 10 Mobile phone.
If you're not participating in the Windows Insider program, you will receive this new app with the Creators Update which is scheduled for release some time in the first half of 2017.