Traveling to Paris

Planes and trains are the opptions.

Or a car or a ferry (ferry to be followed by car, train, or perhaps bus)

From where?

Well you could walk, or rent a bike or a horse.

Go to Rome2rio and put in your starting point and Paris, and you will see various options. You could also book a trip with a tour company.

From where?

Based on OP's other post, presumably London

This isn't something I'd recommend, because you'd have so little time in Paris itself, but the Eurostar train takes about 2.5 hours between St. Pancras Station in London and Gare du Nord in Paris. So five hours of your day are spent riding the train -- plus you have to be there well ahead of departure, so really more like six or seven hours. That doesn't leave much time for Paris, a city worth at least a week or more. Eurostar tickets are not expensive if bought well in advance, but, unlike the Heathrow Express, the purchase commits you to a specific train.

You could also fly, the actual flight time is short, but the time spent getting to and from airports and processing there would add up to much the same, plus a lot more stress.

Based on OP's other post, presumably London.

In that case, the train is the best way to go. Fastest and most comfortable. And the cheapest way for a day trip. Although, while people do it as a day trip, spending a night or two in France is better.