Nikon D3100 will take pictures, but they show up as black?

My Nikon D3100 will turn on and shows color, like if I'm taking a picture of a bed, I can see the bed through the camera. Last night, I unattached the lens from the body to compare weight with another friend's lens, and ever since then, my pictures turn up as pitch black on the viewing button. I take a picture like normal, but it shows up as black. Please no camera lingo, I ave no idea what anything is.

I just have the 18-55mm kit lens

Turn the camera off and take the battery and card out for 5 minutes.
Put them back in and attach the lens properly, Remove the lens cap. Set the camera to Auto mode. Turn it on. This ought to have reset it.
If it doesn't work and you can get pictures from another lens mounted on it then the lens has probably got stuck inside or been damaged. You could try cleaning the contacts too.

Black images shows gross underexposure.

You need to learn how to user you light meter

You also need to learn how to balance ISO, shutter speed and lens aperture.

http://camerasim.com/camera-simulator/

If you have no idea what anything on your camera is, why do you have an advanced cameras?

What a waste…

Did you remove the thingy at the end of your lens?