One of the signature features of Windows 10 is the way it handles systemwide notifications, allowing any app (including desktop programs like Outlook 2016 and Adobe's Creative Cloud) to display messages. The more apps you use, the more chaotic those notifications can get.
Take control by opening the Settings app and going to the Notifications & Actions section:
To turn off all notifications from apps, move the Get notifications from apps and other senders slider to the Off position.
To choose which apps are allowed to interrupt you, scroll down to the section headed Show Get notifications from these senders. Move the slider for an individual app to the Off position to silence all notifications from that app or feature.
For more fine-grained control over how an individual app can display notifications, click the app's entry in the Notifications list. That gives you five options.
The top entry on the list, Notifications, lets you disable all notifications, graying out all the other options.
For control over pop-up messages and sounds, use the Show notification banners and Play a sound when a notification arrives options.
If you don't want the notification panel (formally known as Action Center) to be cluttered up with old notifications from an app, slide Show notifications in action center to the Off position.
Finally, use the Keep notifications private on the lock screen to prevent calendar entries and alarms from displaying when you've stepped away from your desk and locked the screen.