It is important to know the relationship between disks and files. Disks are used to hold from one file to hundreds of thousands of files. Files are placed on disk by encoding magnetic 1s and 0s on the surface of the disk. From the placement of the 1s and 0s on disk, DOS understands the commands and data on the disk and treats it appropriately. Directories are DOS's way of organizing the many files that can be placed on disk.
Every disk has at least one directory.
From the root directory of every disk we are able to directly or indirectly access every file on the disk. The root directory can hold directories or files. Subsequent directories can also hold directories or files, and so on. . . The root directory has no parent directory, but only child directories. These commands provide the most basic functionality for working with files.