On my Sony Experia its settings, apps and notifications, configure notifications, notifications (will show on for all apps) then go to the individual app and set them to off.
No way of locking individual apps unless the app has its own password (very few do) but I would strongly recommend that you set the phone lock, either via PIN or fingerprint (both preferably), you don't want your phone to be open to anyone.
Last edited by andytug; 13th Feb 2018 at 08:10.
Reason: Spelling