The Sensitivity is the amount of change required in the image to increase the motion bar by a percentage.
Sliding the Sensitivity bar to the left will decrease the sensitivity of the motion detection i.e. more movement is required to trigger the alarm.
The best way to configure these settings is to adjust the settings and have someone walk in front of the camera until your feel you are getting the required results.
This trial and error method make take quite long to get right but it’s the best way to obtain good results.
The Threshold is the level that the motion bar needs to reach in order to trigger an alarm.