Every sign-in uses the passkey you registered when you set up your account. There's nothing to type and nothing to remember — just a fingerprint, face check, or security key tap on the device you registered it on.
Why there's no password
A passkey isn't a password that happens to use your fingerprint instead of typing — it's a cryptographic key pair generated on your own device, and the private half of it never leaves that device, not even to us. There's nothing stored anywhere that an attacker could steal, reuse from another breach, or phish out of you, because there's no shared secret to steal in the first place.
Signing in on a device you registered
Just open the sign-in page — your browser or operating system prompts you for the same check you set up with (Face ID, Touch ID, Windows Hello, or a hardware security key), and you're in.
Signing in somewhere else
If you're on a computer that doesn't have your passkey — a new laptop, a shared machine — see signing in from a new device for how the Use my Smartphone option works, without registering a second passkey.