Does the Nikon D3100 have a charger or do you place batteries inside?

Yes I know I sound like an idiot but I'm buying the Nikon D3100. I was wondering if you get a charger and charge the battery or if you buy new batteries to replace the dead one?

Don't worry. The Nikon D3100 comes supplied with a rechargeable Lithium battery (and charger).
Here's an idea for you… Download the D3100 Reference Manual and you can read all about it before you buy it. That way, you won't need to come back here asking us how to use your camera…
http://support.nikonusa.com/...lyaw%3D%3D

Both. It is supplied with a Lithium ion battery that comes with its own wall charger. All cameras use batteries.

This may be something you would want to ask of your camera shop proprietor.

But yes they come with a charger and battery. What is "in the box" is listed here

http://www.nikonusa.com/....TechSpecs

I'm surprised you did not come across this page when doing your research