In order to save an invoice as a template, you'll need to ensure the Invoice has not yet been marked off as Closed, Cancelled or Exported. A few handy things you can do prior to saving the template is to ensure the name of the invoice can be used later down the track Ie. Monthly Retainer
Open up the invoice that you would like to save as a template. From the action menu select the option 'Save Template'. Briefcase will then provide a pop up with the name of the invoice.
Once this has been done you can navigate to the job you are wanting to load the template into. You'll need to create a new invoice and then use the action menu to select the 'Load Template' option.
You will see a list of previously saved templates. Once you've found the template you would like to load simply click on it and Briefcase will automatically bring across any related information from the Line Items.