iPhone 7 and two factor authentication

Set up two-factor authentication for your Apple ID

Two-factor authentication is available to iCloud and iTunes users with at least one device that's using the latest iOS or macOS. Learn more.

You can follow these steps on your iPhone, iPad, or iPod touch to turn on two-factor authentication.

Turn on two-factor authentication in Settings

If you're using iOS 10.3 or later:

1. Go to Settings > [your name] > Password & Security. 
2. Tap Turn On Two-Factor Authentication.
3. Tap Continue.

If you're using iOS 10.2 or earlier:

1. Go to Settings > iCloud. 
2. Tap your Apple ID > Password & Security. 
3. Tap Turn On Two-Factor Authentication.
4. Tap Continue.

You might be asked to answer your Apple ID security questions.

Enter and verify your trusted phone number

Enter the phone number where you want to receive verification codes when you sign in. You can choose to receive the codes b

Two-factor authentication for Apple ID - Apple Support

https://support.apple.com/en-in/HT204915

Two-Factor Authentication does not protect your phone. It protects your Apple ID. While you don't need to have more than one device as the code can be sent to your phone, you certainly should have an additional trusted device or number in the event something happens to that phone.

Two-factor authentication for Apple ID - Apple Support

One the phone, you only need 2FA when you're signing into an Apple ID. Once you've done that, you won't need it again. To protect the information on your phone, use a passcode.

See here:

Use a passcode with your iPhone, iPad, or iPod touch - Apple Support

Glad it helped!

I would like to have two procedures for singing in, to be sure the iPhone is safe. Can the Touch ID be used with the passcode to sing into the iPhone 7? How do you do this?

Or, if I should choose to use Touch ID only to sign in, rather than the passcode, which is asked for, how do I do this?

If you're going to enable TouchID on your phone, you are required to enable the passcode first. TouchID will not unlock your phone when you restart it or if you haven't unlocked for twenty four hours. So, if you have TouchID enabled, you will always have the option of using it or the passcode.

You can certainly set a more complex passcode than the six digit passcode. But, you will never be asked for more than one thing to unlock your iPhone.