What is a long exposure shot, and can you do it on a NIKON D3100?

--
I want to take a sparklers shot, where i write my namee,
how do i do iT!

Yes, you can do it on your D3100 (and on any other camera that lets you control shutter speed). Here's how you do it.

http://www.diyphotography.net/painting_with_light

Set the camera to shutter priority. Turn the mode dial on the top right hand side of the camera to "S". Now here I'm only guessing… But I imagine the dial at the back of the camera where the thumb naturally sits will adjust the length of the exposure.
I don't know what the rule is about when hand held is not recommended but I guess I would say that if you are playing with longer exposures you should get yourself a nice tripod.

You asked this question a couple of hours ago