Get your ticket from one of the easy to use ticket machines in Centraal Station and then just hop on the train! At the ticket machine you can press on the British flag for English and then a 2nd Class, Full Fare, Valid Today ticket is your best option.
The trip to Haarlem can be a relaxing way to to see a bit of the typical Dutch landscape from the comfort of a train. If you are on a train that has two decks, make sure to go upstairs to get the best views. The left side of the train will give you the best view of the centre of Amsterdam as you leave and then of Haarlem as you enter.
On the short trip, you will pass a lot of cool Amsterdam neighbourhoods that most tourists dont see. Before you know it, the train announces “Station Haarlem”. Look to the left side of the train to see the round dome that is the local prison, the Spaarne River, the windmill and the tower from the Grote Kerk in the centre of town. When you hop out, follow the signs for CENTRUM...
Then you're ready for the coffeeshops of Haarlem!