Each user will have their own home directory created by the system administrator. When you log on using a Telnet session you will be placed in your home directory. Your home directory is actually a sub-directory of a larger structure, a single tree representing the whole of the Unix file system. The root directory is the start of the tree. This is a convention that makes it easier to manage the disk.
Every file has a filename .
The Unix operating system is case sensitive so JAN, Jan, jan would be three distinct filenames. The filename you choose should mean something. The filename should convey information about the contents of the file. A filename extension is the part of the filename following a period. The ls command lists the contents of a directory.