By train: You can take a train from Brighton to London St Pancras International, and then take the Eurostar to Paris Gare du Nord. From Paris, you can travel to other parts of France by train or bus.
By plane: You can fly from London Gatwick Airport to various airports in France, including Paris Charles de Gaulle Airport, Nice Côte d'Azur Airport, and Lyon-Saint Exupéry Airport. From there, you can travel to other parts of France by train or bus.