Sign-up needs an invite code from the owner. You start with no portfolios; the owner chooses which ones to share with you.
Your email is your user ID. Face ID, a fingerprint or your device PIN signs you in, with no password or code to remember.
No passkey on this device? Use a password and an authenticator app instead.
Next you will set up an authenticator app (Google Authenticator, 1Password, Authy and the like). Every sign-in asks for its code.