All the information regarding dress codes are given in the brochures that are sent to you, usually 6 weeks before your voyage. Have a lovely trip.
Usually, the seadays (excluding 1st/last night) are formal nights, the shore days are informal nights. Formal = dinner jacket for man, evening wear for woman. Informal nights = jacket and tie for man, less posh evening wear for woman (eg smart trousers and glitzy top, or less revealing dress). There is an expectation to dress for dinner for the main restaurants, but don't have to if you eat in the Lido.