Pushing the pedals has an article showing Olivia practicing using the tool.
As Daniel from the above link stated: You may be wondering why anybody would even want to remove their cassette while on tour. The purpose is to allow the replacement of broken spokes in the rear wheel. The rear drive-side spokes are the most likely to break due to the higher tension and torque from the drivetrain.
You may in the worst case need to replace your cassette.