You will be charged automatically after the including 45 minutes have passed.
With extended rental you can have the bike for 6 hours, in addition to the included 45 minutes. After 45 minutes it costs 5 NOK per 15 minutes.
Does the money get drawn from my account automatically?
Yes, if you turn on extended rental. You'll always have a good overview over how long you have been out for a ride and when extend rental starts in the app.