You drive onto the train and squeeze up close to the car in front. Switch off the engine. You now have a 35 minute crossing during which you have very little to do. Each carriage holds four or five cars, and the same upstairs. You could go and make friends with the other drivers, fall in love with the beautiful girl in the sports car, and have a barbecue with the people behind. But it isn't going to happen.
There's a loo - the world's tiniest - every three compartments. So you can stretch your legs, do a bit of queueing, and take a leak. You can wander up and down and look at the cars. Er, that's about it.
It's a good idea to take a picnic - it helps to pass the time. Take a book or a magazine as well. There isn't even a coffee machine on board the train.
But the great thing is that you are only on the train for 35 minutes. It pulls into the station, you set your watch back an hour, and set off - straight onto the French motorway system. They have already had the opportunity to see your passport on the other side, so there are no delays - just set off.