I have a nikon 5100. The lenses have a on/off button and two others. How and when do I use them?
This is the 18-55mm lens? That lens only has a "A-M" switch to go between auto and manual focus. Some lenses have an on/off switch for the Vibration Reduction (VR) feature, and some of them have another switch to turn on/off active VR.
Vibration Reduction compensates for camera movement. This lets you hand-hold the camera at slower shutter speeds. Active VR allows camera movement in one direction while compensating for movement in other directions, allowing for panning.
You can download the manual for some (though not all) Nikon lenses from