Tap an invoice to open it. Changes only stick once you press Save invoice.
Prints at the top of every invoice. Default rates fill in on each new invoice; you can still change them on a single invoice.
These show in the Bill To list. A new customer typed on an invoice is added here when you save it.
Invoices save online automatically, and a copy is kept each day. This is an extra copy for your own records if you want one.