Do i have to buy anything extra for my fisheye lens to work for my Nikon D3100?

I bought a Precision Design 0.25x Super AF Fisheye Lens and i'm wondering if i have to buy anything extra for the lens to work with my Nikon D3100

No. You just need to screw it onto the front of your kit lens as it isn't an actual lens. You may have some issues with your focus if it is a particularly poor quality one, but otherwise? You're good to go.

You may have to buy a step filter adapter if the thread sizes are different.

Precision Design 0.25x Super AF Fisheye Lens can be a great tool for real estate agents or for just having fun! If you plan on doing panoramic or full room shots, just stand your tripod in a corner facing the center of a room. It can capture almost EVERYTHING, floor to ceiling, wall to wall, except what is directly behind the camera. Just import the resulting image into a panoramic editor or "stitching program" (your digital camera probably came with one), convert it to a QuickTime VR file, and have a virtual view of the room.