On the 24th, some (not all) restaurants will be open in the evening. Reservation is usually required. All shops will be open.
On the 25th, you can expect all shops, sites, museums to be closed except on very touristic places like Champs Elysées. Many restaurants will be closed mostly on 25th evening.
If you stay in a high-end hotel, they will for sure serve food on the 24th and 25th.