With your smartphone
Use the Oslo City Bike app to see the location of available bikes at any given moment. This is available on both iPhone and Android.
Go through these simple steps while being close to a station in order to unlock a bike:
See to that the station shown in the app, is the station you're at (if you're placed at another location, check out this guide)
Press Unlock bike
The app will show you which of the locks you'll recieve the bike from
Lift the bicycle out of the station.