Sign Up creates a real Director account: your organization's name, your name, an email, and a password (or sign up with SSO instead of a password). That account signs in at /login going forward.

From there, invite Floor Admins by email from the Team page — they accept the invitation and sign in via SSO, landing with Floor access to your organization automatically. There's no separate role to pick anywhere; it's determined entirely by whether someone arrives via a plain signup or a valid invitation link.