The compass setting controls whether the screen rotates automatically as you do (dynamic), or if you must rotate it manually (static).
To rotate the screen with the dynamic compass, simply rotate your body while holding your scanner. The scanner will use your device’s magnetometer to orient the view dynamically as you rotate. To rotate the screen with the static compass, swipe on the screen with a single finger. The Settings menu permits you to toggle between dynamic and static compass.
Unfortunately, the dynamic compass doesn’t always work very well; many devices fail to orient the view to line up with the direction you are facing. You can attempt to calibrate the magnetometer by standing as far away as you can from sources of electromagnetic interference (televisions, computers, power lines, cars, etc.) and moving the device in a figure-eight pattern in front of you while rotating the device in your hand. This might improve the dynamic compass behavior, or it might not.