https://support.google.com/accounts/answer/185833?hl=en

Sign in with App Passwords

Tip: App Passwords aren’t recommended and are unnecessary in most cases. To help keep your account secure, use "Sign in with Google" to connect apps to your Google Account. 

An App Password is a 16-digit passcode that gives a less secure app or device permission to access your Google Account. App Passwords can only be used with accounts that have 2-Step Verification turned on.

When to use App Passwords

Tip: iPhones and iPads with iOS 11 or up don’t require App Passwords. Instead use “Sign in with Google.”

If the app doesn’t offer “Sign in with Google,” you can either:

• Use App Passwords
• Switch to a more secure app or device

Create & use App Passwords

If you use 2-Step-Verification and get a "password incorrect" error when you sign in, you can try to use an App Password.

1. Go to your Google Account.
2. Select Security.
3. Under "Signing in to Google," select App Passwords. You may need to sign in. If you don’t have this option, it might be because:
   1. 2-Step Verification is not set up for your account.
   2. 2-Step Verification is only set up for security keys.
   3. Your account is through work, school, or other organization.
   4. You turned on Advanced Protection.
4. At the bottom, choose Select app and choose the app you using -> Select device and choose the device you’re using -> Generate.
5. Follow the instructions to enter the App Password. The App Password is the 16-character code in the yellow bar on your device.
6. Tap Done.

Tip: Most of the time, you’ll only have to enter an App Password once per app or device, so don’t worry about memorizing it.