Totals by the member's EU country, in euro, net of VAT, and the VAT you charged them. A month with no EU sales is still marked — the return is due even when it is nil.
Frontier does not file or pay. The return and the payment go through the tax portal of your member state of identification; this records the figures and the day.
The return charges each member's own country's standard rate. These start from one published table, dated; a rate used in a return must have been confirmed by you within the year.