How to set a camera to take pictures like this?

I have a nikon d3000, and i want to know what setting to put it on or possibly how to edit my pictures like this:

i like the exposure and dark background

Ouch… That is simply a straight on flash.

Set your camera to Auto, get close to your subject and chances are you'll get exactly that… Harsh shadows and an under exposed background.

I'm amazed that you're trying to COPY that, rather than learn to avoid it.

It's flash off to one side and slightly higher than the camera, look at where the shadows are and reverse it and the catch-light in her eye.

When taking flash pictures you're taking two exposures at the same time. The ambient component and the flash component.

To get a dark background you expose to make the ambient light dim or even to black by using low ISO, a small aperture (f11 or even f16) and the fastest shutter speed you can use and expose all of the sensor to the flash (the X speed, usually around 1/160th to 1/250th depending on camera) if you turned the flash off and took a shot this setting would give you a black frame.

Now introduce the flash set on manual and adjust the flash power and flash to subject distance to give you a good exposure on the subject, make sure none of the light from the flash can hit the background, If your subject wears black you get the Mappelthorpe 'floating head', results are like this

Shot's like this are not done in editing they are shot that way.