The Basic Settings in Invoice Options consist of 4 options.  Contact Name - By default, the customer address at the top of the invoice will just show the company name.  If you'd also like the contact name to be included too then tick this box.  You can configure the Contact Name in Customers> Choose the Customers> Contact Details> Contact Name.  'Email Sent' Icon - We can display an icon on the Sales page to indicate that an invoice has been emailed.  This can help you easily identify any invoices that you haven't yet emailed to the customer.  Prev/Next Buttons - Enable 'Previous' and 'Next' buttons on invoices and decide if they should loop through all invoices, or only invoices for the current customer.  You will find these buttons at the bottom when you're viewing the invoice.  Payment Method - If most payments you receive are by a specific method, i.e. Cash, then you can set this to your default method so that when you are adding payments to an invoice the method is already set for you.  You can add/remove these in Settings> Payment Methods.