The situation at Schiphol
Amsterdam Airport Schiphol has one terminal. Its ground floor is for arrivals (its first floor for departures). The map below describes the situation on the ground floor: Schiphol Plaza is the central hall of the terminal and there you find the ticket-windows of NS (the Dutch Railway Company often recognizable by its symbol: ).
Schiphol's Railway station is below Schiphol Plaza; you can get there via elevators in Schiphol Plaza.
The area below the dotted line is the shopping area (Schiphol Plaza); the area above the dotted line is only accessible for passengers.