How to light paint with a Nikon D3100?

I use it mostly for film, because that's what i do, but i want to try light painting and i know the camera is capable. Please walk me through how to do this! (Besides be in the dark with lights, and a tripod) So essentially changing the exposure/shutter whatever to let me do the painting!

With Film its hit and miss, practice with a digital camera, then use that as a guide.

Walking you thru step by step is lazy on your part. Have fun with it.

It is called "light graffiti".

Put your camera on a tripod, and use either the self timer or an external shutter release.
Set your camera to a long exposure (say between 15 and 30 seconds, although you might want it much longer than that, depending on your project).

Refer to your manual if you don't know how to do something - you should know that book inside out, anyway (if you lost it, download a new one from the manufacturer).

Make sure you are in a very dark room/area. It helps to have an assistant dressed in dark clothes - less chance of showing up in the shot. Use pretty much any light source you can think of, experimenting with it is fun. Also play with different ISOs and apertures to see the differences there. It will turn out a good learning experience, as well.

So once everything is set up and ready, click your shutter button/timer and have your assistant move around with the light source. Have fun trying to make different designs, all the way from some random squiggle to carefully planned and executed designs.

P.S. Some people call it "painting with light" which is actually a very different technique. Here is an amazing video about it: http://fstoppers.com/night-photography-how-to-paint-with-light/