my first europe trip is coming up in two weeks and i'm wondering if i should buy train tickets in advance online, or wait and get them at the station. i'm still a little confused about the whole "reservation" thing, but i think i might need them for [Brussels to Amsterdam] and [Amsterdam to Paris] and should then get them in advance. any advice? if i buy a ticket on a "country" website listed at ricksteves.com, does a reservation come with it? thanks!
For that route, you will need a reservation if you're riding a Thalys train. I believe reservations are included with your ticket, as they are compulsory.
For regional trains, you're not usually required to have a reservation, if reservations are possible at all. For some routes/days, you may want to get reservations, but I'll let some of the more knowledgeable posters fill you in on that.
If you're buying point-to-point tickets and are comfortable with locking yourself into specific times/trains, buying ahead is a good idea, because there are usually good deals involved when you buy ahead of time. The more flexible the ticket's conditions, the more expensive it's going to be.
For the high-speed Thalys link between the three cities you mentioned, your ticket includes a reservation. Trains usually don't sell out, except around certain holidays, so you don't need to pre-purchase a ticket. However, there are a limited number of discounts available for advanced purchase.
If you take the normal ICE train (slower than Thalys) between Brussels and Amsterdam, no need to purchase in advanced. For any other routes within the Netherlands and Belgium, likewise just buy your tickets on the day of travel at the train station. Reservations are not possible for Intercity or Interegional trains within Belgium and the Netherlands.
Since May 1 is a holiday in much of Europe, trains may be more crowded than usual. If your train travel is around that time it would probably be a good idea to go ahead and buy your tix online now.