The best way to travel in Amsterdam is by tram. They are frequent, fast and dependable.
Where to buy tickets?
You can buy a single ticket (€2.80) from the driver, the conductor at the back of the tram, or a machine in the middle of the tram, depending on the sort of tram it is. However, it is considerably cheaper if you buy a 24/48/72/96-hour ticket from a GVB Tickets & Info kiosk beforehand. Prices vary from €7.50 (for 1 day) to €33 (for 7 days).
The GVB day or multi-day travel ticket provides you with unlimited travel through Amsterdam - day or night - by bus, tram, and metro, for exactly the number of hours that best suits your plans. It becomes valid when you first check in.