When a new user is added, it temporarily gives them a password of "booking".
The first time they login, they will be automatically directed to their Edit My Details page where they will need to set their own password before being able to proceed.
The new user password default can be changed to something else if required (Go to Administration - Users - User Manager, and select ' Default Settings'
If your are using another user authentication method (ie. Office365, LDAP or GoogleSuite), then you users will use there network credentials to login.
If they ever forgot their password, there's an option on the login page where they can reset it themselves. Alternatively, this can be done by an admin in User Manager.