Museum Nacht is an once yearly event hosted by many of the museums here in Amsterdam. The Museums will be open late and there will be live music and general entertainment happening at all locations and underway.
Tickets are 18,50euro and can be purchased online here.
Alternatively you can also purchase them at shops where you see a sign Primera which has about 450 locations in Amsterdam, usually at small little shops around the city. Typically you can not do day of purchases at the Primera shops, usually.
Also there seems to be tickets but it always sells out the day of so don’t hesitate if you want to go.
The event its self will take place on Saturday November 1st from 1900-0200, and that usually means the museums will close early on the day to prepare for the night’s activities.