booking a couchette

I'm not sure I understand this question, but I'm following, because I, too, have a couchette question, that I will post soon, if this one doesn't supply me with the answer.

No, but you need a ticket to book a couchette.

I am curious. What is a couchette?

I am thinking that maybe it has something to do with a flight or on a train / ferry or a lodging.

A couchette is a type of sleeping compartment on a night train. The Man in Seat 61 explains it: https://www.seat61.com/sleepers.htm

It's a padded ledge, usually in a compartment for 4 or 6 people. It's normally the least expensive option for spending the night in a horizontal position on a train.

it is pronounced as in French as koo-shette, not couch-ette despite the spelling

so it is kind of what we call a Roomette on Amtrak? Great way to travel around Europe.

Thank you all for your information.

Now I have also discovered The Man in Seat 61.

from what I can see a Roomette is way fancier.

Roomette - one or two people, actual chairs and beds, first class.

Couchette - up to 6 people, stacked bottom-middle-top bunks in two stacks, on basically narrow shelves, no furniture, second class.

Neither Canada or the US have any equivalent to European style Couchettes.

They are not segregated by sex, and you sleep in your day clothes.

The UK has never had them for public use, although the staff cars of the Royal Train has them. Also the continental section of the former boat trains from London to Europe (through trains which crossed the English Channel by ferry) used to convey couchette cars, attached at the Channel ports in France.

If you want to make things complicated get a Eurail Global Pass. If you want to keep it simple just book ticket+resevation directly from the company running the train.
And if you want a bit of comfort, get a sleeper, not a couchette.

That depends where you are doing this booking.

If at the train station in person, yes, you need to show the staff person your Global Pass...that's what I do. When I am asked if I already have a ticket, I say I have the Pass, almost always I don't need to show it...they believe me and I only buy a seat reservation, no sleeper or couchette option.