Hi,
1. It can work without. Remove the "address" view and it will work.
Or you can also force the menu item of the checkout to registered users so that Joomla will first ask you to login or register before accessing the checkout, and when you access the checkout, you'll be able to fill in the addresses and finish the checkout.
2. It allows the customer to enter his billing and/or shipping address. For that, it requires first the customer to either:
- be logged in with a user account
- have filled his email address on the guest form of the login view
Before either one of these conditions are met, the address view doesn't display anything. However, if you try to finish the checkout without an address filled in while you have the address view in the workflow, the address view will block you and should normally display an error message.