Enter your work email and the app finds your workspace for you, then asks for your password. It is the same login you use in a browser, and nothing to do with your Apple or Google account.
Staying signed in
Face ID or fingerprint unlock is optional and lives under More. Your session is held in the phone's keychain rather than ordinary storage.
No signal
The app keeps a copy of what it has already loaded, so a basement with no signal still shows you the address you are standing outside.
Anything you change while offline is sent when the signal comes back.