Coming to Paris by train from the north (northern Germany, Belgium and the Netherlands), you'll probably arrive at the Gare du Nord, also called simply Paris-Nord, in the northern part of the city (map).

Some trains from London—including the Eurostar through the Channel Tunnel—arrive here as well.

Gare du Nord is on the RER Line B suburban train line, meaning that you can take an RER train directly north to Charles-de-Gaulle Airport, or south to Orly Airport.

RER Line D trains also stop at Gare du Nord.

For other destinations in central Paris, its probably cheaper to take the Métro from the Gare du Nord Métro station (Line 4).

Gare du Nord and Gare de l'Est are only a short walk from one another. You can walk between them in 10 to 15 minutes (map).