Relief! I got my sncf tix in the mail!
 

In my confusion, I booked tickets on the sncf website that were only able to be mailed (but not to the USA). (Librys one-way tickets since I waited too long for the smilys fare). Somehow I entered my street address but the country was Pays Bas (Netherlands). Against all odds, they arrived today in the mail!
Now can someone please tell me how to board the train in Amsterdam. We are in (car?) 16 and seats 37 and 38. Do we just walk up to the train and board or do we need to check in? We will each have a rolling carry-on suitcase and a day-pack. Where does the luggage go, or will it be easy for us to figure out? Since we will be in Amsterdam, we should be able to easily get some English-speaking help if we're confused, correct?
I am just so relieved they came today.

Each Thalys car is clearly labeled on the outside - car 16, etc. and there will be a Thalys staffer hanging around the entry doors - there will be no problem - there even may be a chart of the train somewhere on the platform that indicated the train make-up so you know where to stand ahead of time. Since the train starts in Amsterdam it should be sitting there for a while before leaving.

Thalys at Centraal usually leaves from track 14a - but check the BIG board in the main hall about 20 minutes before time to see exactly which track and which -side- of the track...

You arrive at the track, and look for the car# on the side of the car. You climb on -if your luggage is larger than a roll-a-board (21") you need to stash it at the end of the car where there is luggage storage. Smaller bags can go on the rack over your head.

There is no check-in like at the airport - you just get on and sit down. The conductor will eventually come around to examine and stamp your tickets. You might need to produce your passport for id. It might take him a while to get there, don't worry.

In my experience the seat numbers are odd on one side and even on the other, so a window/aisle would be either 37-39 or 36-38, for example. But I could be wrong. The seat numbers will be on small plaques probably on the rim of the overhead luggage rack, or similar place.

If you want, you could ask someone else who's waiting on the track if you are in the right place - show them your ticket if they don't understand (but English is widely spoken in Amsterdam).
There will be a sign hanging over the track that has the track number, the starting point, the ending point, and all the points in between, and the departure time. It might not update until 15-20 minutes before the train is due.

I meant to also tell you that you can go to the 'bar car' and buy a couple of metro tickets (if you're going to Paris) from the bartender. That way, you can get the heck out of Gare du Nord without stopping to buy anything.

THANK YOU! I really appreciate it.

Or get out of Gare du Nord without being pickpocketed!

As a side-note, I ordered tickets for Ams-Paris for May (Smilys) and took the insurance. That only leaves the option of 'mail' so I put in my home address and yes, they came yesterday, to Florida. Someone had marked out 'Pays Bas' (Netherlands).

This is 2 out of 2 times I have rec'd in the mail (within 10 days). I'm not saying you SHOULD do this, but I've been lucky. If presented with option to "print" I would certainly prefer that. I've also picked up tickets at SNCF boutique, not painful at all. I make the best of whatever option applies at the time of the booking.

I don't like the Thalys site - last time I tried to use it, everything reverted to Dutch when the booking commenced. I'm getting used to the SNCF site so I prefer to use it when I can.