Android 5.1 vs Android 6: Notification Bar Settings
When you unlock into Android 6.0 the entire experience looks almost the same at first glance. Nothing on the main screen is too different, but there are changes.
The notification pulldown bar is mostly the same, but swipe down with two fingers to see what's new.
You'll notice a new "Do not disturb" quick setting in Android M. Tapping this turns off all notifications, even alarms, but lets you customize everything. The do not disturb mode has been improved with more user control with options for total silence with zero notifications, only allowing alarms to go off, or a customizable priority mode where only select contacts will be allowed through.
I use this while sleeping, only letting very specific contacts actually send out notifications alerts.