The touch screen fits in the lower or bottom half of the Nintendo 3DS. It is stuck on top of the lower LCD (the part that lights up and shows the image) with a frame of adhesive, like a sandwich. If you tried to re-calibrate it through the 3DS menu, and it still doesn't respond correctly or at all, or is simply cracked or scratched badly, replace it!
The lower LCD is not included -- see link below to purchase that separately. Outside professional installation recommended if you are not a handy, DIYer. If you wish to install yourself, you will need a special tri-wing security driver tool to get inside the Nintendo 3DS. Once inside, you will need a tiny phillips screwdriver.
Also, check our FAQs under Information to see tips on doing the repair.
Please note this part fits the Nintendo 3DS, not original DS, DSL, DSi or DSi XL.