Microsoft 365 (Office) is a free app, sometimes referred to as the dashboard app, from where you can reach your OneDrive documents and start either the online apps or the locally installed Office applications. Microsoft 365 (en-us) refers to a local installation of Office, tied to a subscription.
A Microsoft 365 subscription includes premium Outlook features like an ad-free interface, enhanced security, the full desktop version of Office apps, and 1 TB of cloud storage.