Understanding passkeys

A passkey is a modern alternative to a password. Instead of typing an address and a complicated password, the site can offer:

Sign in with a passkey
        ↓
Face ID
        ↓
Signed in

Apple states that passkeys use cryptographic mechanisms and are designed to resist phishing.

When to use them?

If a reputable service offers to create a passkey, it is usually a very good option. Your Passwords app can keep passkeys just as it keeps passwords.