In-call audio. When you’re on a call, the Volume buttons control the volume of the other person.
Media. When you’re not on a call, the Volume buttons control media volume during playback or before you listen.
Phone ringtone, notification sounds, and alarms. To adjust these volumes, press a Volume button and then use this shortcut on your home screen:




You can adjust the volume of each app.
Also, your phone can learn to automatically mute apps you usually mute. You can review and adjust the list of apps at any time.


Slide to adjust the app's volume.

If you don’t want your phone to learn your usage patterns and automatically mute apps, go to Settings > Sound > Multi-volume and turn Auto mute off 
To silence a ringing phone, press either the Power button or the Volume down button.
To switch to vibrate at any time, press & hold the Power + Volume up buttons until you feel a vibration and see 
If you want to customize Power & Volume up so that it silences the phone instead of vibrating:
You can simply pick up your phone to silence incoming calls and alarms, and to turn vibration on.
To enable this gesture: