How do I turn on two-factor authentication?

In Settings, find Two-factor authentication and choose Enable 2FA. Scan the QR code with an authenticator app such as Google Authenticator, Authy or 1Password, then enter the 6-digit code to confirm.

Save the recovery codes you're shown. Each one works once and lets you sign in if you lose access to your authenticator app.

Settings also lists recent sign-ins, and you can sign out on every device if something looks unfamiliar.