In all public transport in Amsterdam (tram, bus and metro) you can travel with a "Strippenkaart" (public tranport card). It is possible to buy tickets in on board, but if you plan to use public transport more than once, it's wise to buy a public tranport card in a tabaco shop or at the main bus/train stations. A card for 7 rides (15 strippen) costs about € 6,- and can be used by more than one person on the same ride. Just tell the driver or conductor where you want to go and how many people will travel on your card; he will stamp your card (number of zones + 1).

Trams and metro run mainly between 7.00h and 00.00h
Outside these hours nightbusses and taxi's are available (night fares).