Carbon paper is placed between the original and a blank sheet to be copied onto. As the user writes or types on the original, the depressions made cause the ink to be deposited on the blank sheet, thus creating a "carbon-copy" of the original document.
Use of carbon paper has been mostly superseded because of electronic means such as photocopying, however, it is still used in situations where instant copies of written documents are needed, e.g. for receipts at point of sale or for on-the-spot fine notices.