1. Eurail is the combination of the national rail companies in 21 European countries. A Eurail pass is honored on all transportation run by the national rail companies in those 21 countries (or the subset of them you choose). That’s just about every train in those countries. The exceptions are Eurostar and some privately owned scenic railroads in Switzerland.

2. Eurostar is the chunnel train between London and Paris or Brussels. Eurostar is not covered by a railpass, but that doesn’t seem to be an issue for your itinerary. Price Eurostar tickets at www.eurostar.com

3. Thalys is simply the made-up name (it’s not a word in any language) for the fancy, high speed trains between Paris and Benelux. Your railpass will be your ticket for the Thalys trains, but like many premier trains, Thalys requires a reservation. Your railpass does not cover the reservation, so you’ll have to pay extra for that.

If you don’t use a railpass you can buy a ticket for a Thalys train at the station or from www.Thalys.com or from the French, Belgian or Netherlands national rail company websites.

4. Trains a relatively expensive in France and Benlux, so a pass will usually save money for the typical tourist. However, if you’re willing to search out advance purchase and other on-line specials on the individual national rail company websites you might be able to be able to “beat” the railpass. You’ll have to commit to non-refundable tickets for specific dates and times up to 60 days in advance and you may not be able to buy tickets for all of the routes in your itinerary on-line.