By tapping on the plus sign you will create an invoice.
The invoice is created by setting which customer you want and which project to include.
If you want you can create one invoice from all the projects on a customer.
The projects will then come up as one line per project on the invoice.
You should then choose the startdate and enddate for the invoice. This will be used for the selection of the times that will be included.
Invoice date and Due date is just what it says.
Comment is a text that will appear on the invoice, so you can add a comment for the customer to see
Invoice is paid is used later to mark the invoice as paid when you have got payment for the invoice.
Reference is the customers reference, if you don't enter anything here, the contact person on the customer form is used
When you are finished you tap on Save.