How to disable Notification Sounds and System Sounds on iPhone?

Instructions for iPhone

To disable System sounds:
1.   Go to Settings
2.   Tap on Sounds & Haptics
3.   Disable Keyboard Clicks and Lock Sounds – move sliders from right to left (slider icons will be greyed out)
You can also customize other sounds in the Sounds & Haptics menu, for example turn off the sound of Reminder Alerts. To do it, tap on it and on the next screen choose Alert tones - None.

To turn off notifications for selected applications:
1.   Go to Settings
2.   Tap on Notifications
3.   Select the app (for example App store app) and tap on it
4.   You can turn off notifications by moving slider from right to left (slider icon will be greyed out)
5.   You can disable only the sound of incoming notifications, by moving the Sounds slider from right to left (slider icon will be greyed out)

Find more detailed instructions here:
How to disable Notification Sounds and System Sounds on iPhone