The trams, buses and metro lines run from 06.00 in the morning to 00.30 at night. Between 00.30 and 07.30 in the morning, you can use the night buses. GVB 24/48/72/96 hours tickets are also valid on night buses. If you do not have one, you can buy a GVB nightbus single ticket from the driver.
The night bus leaflet with a map of all night bus routes is available for free at GVB Tickets & Info on the Stationsplein.
Look at the tickets and prices overview of the nightbus.
And check out the network map of the night lines.