Connect the Kindle to the computer, set the required classified folder (such as "DK_Documents") in the folder where books are stored, and then put the books to be classified into the classified folder (books outside the classified folder will also be displayed on the home page, so you can put the books you are reading on the home page for easy viewing). After sorting out the books on the computer, and then returning to the Kindle, all the messy books will disappear and be replaced by neat classified folders.