When you restart an iPhone to the white screen with "Hello" in different languages, it does erase everything on it. If you save everything to your iCloud account you can just log back in and it should be fine, but your phone will be as if you just bought it. Here are the steps:
-Tap Settings > General > Reset.
-Tap 'Erase all content and settings'
-Enter passcode/Face ID/fingerprint.
-Tap 'Erase iPhone'
-Enter your Apple ID password.
-Your iPhone will now factory reset.
***if you just want to shut it down, hold the volume and power button at the same time until the screen goes dark. then turn it back on. this doesn't erase anything and does not reset your phone to the white screen with "hello"***
I hope this helps you! Good luck and have a great day. ❤️