Kathy not being able to find Paris Nord to somebody who has been to Paris is a bit like saying you can't find the Eiffel Tower (and contrary to what I was accused off elsewhere I am being jocular, not snarky). Paris has a number of main stations, Paris Gare du Nord (shortened to Paris Nord), Paris Est, Paris Gare de Lyon etc. Gare du Nord is the largest, and (unsurprisingly from the name) serves destinations north of Paris.
It has a big Métro and RER station called "Gare de Nord" underneath it so you can get to it from anywhere in Paris.
A photo of the inside of Gare du Nord is here. A close up picture of a Thalys train is here . Each train has a capacity of around 750 passengers.
"Port de Javel Bas" is just south of the Eiffel tower. The cheapest way to get to Gare Du Nord is by Métro/RER. But if you have a lot of luggage, or there are many of you, or you are a first-timer who is not sure of the Métro, then you could take a taxi.
Note main railway stations for a city are in the centre of the city, just like "Bruxelles Midi" which is where your Thalys will stop. One advantage of high speed trains is that they travel from city to centre, you do not have to waste time getting out to an airport.