When files are created on a filesystem they are stored inside a directory. A directory is simply a file that has a particular format. It is stored on the disk in the same way as ordinary files. The only reason you can't edit them like an ordinary file is because the editor programs (such as vi) specifically stop you from doing so. We will use the directory /var/adm as an example to demonstrate the structure of a directory.
As you know, the ls command is provided to list the contents of a directory:
hydrogen# cd /var/adm hydrogen# ls aculog log passwd sulog utmpx wtmp lastlog messages spellhist utmp vold.log wtmpx hydrogen#
This has shown us the names of the files and directories that are in the directory /var/adm, but ...