Android Marshmallow, like Lollipop before it, also lets you choose to block apps from sending notifications entirely, or to mark notifications from certain apps as priority notifications.
First, head back to Settings > Sound & notification. Next, scroll to the bottom and tap App notifications, then tap on the app for which you want to adjust notification settings. Toggle the Block all slider to the “on” position to stop receiving notifications from that app. Toggle the Treat as Priority slider to “on” if you want notifications from that app to be considered Priority notifications.
Also if you have do no disturb mode on you will not get any notificatiuons so make sure that is not on.