A Guest account will allow you to request your booking without setting up a password to login to Hallmaster with.
You can setup a password later if you wish using the 'Reset Password' link on the login page.
You won't be able to login and view your bookings and invoices until a password is setup.
Your account won't be secured with a password, and therefore can be used by anyone that knows your email address to request bookings.
If you are going to be a recurring customer for this venue, then we would recommend setting up a password now to avoid having to re-enter your details later.