Zaandam Centraal Station has direct connections with many big cities from the Netherlands, such as Rotterdam (IC 1h 30 minutes), Den Haag (Spr 1h 10 minutes), Maastricht (IC 3 h), Eindhoven (IC 50 minutes), Alkmaar (IC 15 minutes), and, of course, Amsterdam Centraal (IC 13 minutes). NS is the Dutch railway system app that offers information about train routes, schedules, and prices.
Coming from Brussels or Antwerp Central Stations, as well as from Brussels airport, is quite easy since is a direct train, direction Hazeldonk, which takes 2 hours and 40 minutes, respectively 2 hours and 50 minutes, to arrive at Amsterdam Centraal, from where you can follow the steps above.
To arrive in Zaandam from Dusseldorf first requires taking a Sneltrein R13 from Dusseldorf Hbf for 1 hour and 8 minutes to Venlo (8 stops). From Venlo there is an Intercity train to Schipol Airport, which takes 2 hours and 8 minutes, and finally from there a Sprinter for 17 minutes to Zaandam Central.
For international trains, companies such as Thalys (Paris, Brussels) and Eurostar (London, Brussels) are also options, that stop in Amsterdam Centraal.