How do I transfer passwords to new iPhone?

Hello!

I'm assuming you're going from an old iPhone to a new iPhone. If you are using an Apple ID then your passwords are automatically carried over to your new iPhone. Just make sure that the Keychain is enabled. Follow these steps to check it.

1. Tap Settings, tap [your name], then choose iCloud.
2. Tap Keychain.*
3. Turn on iCloud Keychain. You might be asked for your passcode or Apple ID password. 

This article describes step by step how to turn on the Keychain.

Set up iCloud Keychain - Apple Support

Create a full encrypted backup of your old device via computer, as per these instructions:--> About encrypted backups on your iPhone, iPad, or iPod touch - Apple Support, then restore data from that backup.

Regards

Giulio