Secure passwords are long and complex. Unfortunately, this also makes them difficult to remember and, especially on smartphones and tablets, very awkward to enter.
With WebAuthn you can log in completely without a password. This can be a smartphone, a current Windows 10 device or a small USB/NFC stick. On the smartphone, this works just like unlocking, for example via fingerprint, facial recognition or a swipe gesture. And on desktop computers, for example, with a USB token. If you get a USB hardware token like a Yubikey, you can use this one key both on the desktop (via USB) and on the smartphone (via NFC) to log in.
This is much faster than typing in a password. And it's even more secure.