How to connect a camera the computer?

Hi, how do you connect a Nikon D3100 to the computer so that i can control it and see what is seen through the lens?
Any software, cables?

There should be a USB cable that came with it. If there was a disc, install the software first, if not, then just hook up the cable, and you will be able to from there, you will also be able to review pics from here.

Don't know about a computer, but I use a small jack plug from my camera to the yellow socket on our TV ( video games ) to get that result. Works a treat.

This is called,'Tethering.' You can check on Nikon's website, but only a few DSLRs can do this and I'm not sure that the D3100 is one of them.