This video shows you how to generate pre-formatted invoices
This video shows you how to create complex products / Build of materials. These can either have a FIXED cost or a variable cost. These will display as a single line on the customer invoice, bit display as multiple items on the user interface. Example here would be a bitch spay. This you may want a single line on the invoice, but it is made up of multiple items such as GA, hospitalisation, antibiotic injections, suture materials, pain killers etc.