Be prepared for a lot of output with common names. You can also specify the loginID to find the person's full name. An obsolete program to read and send mail. Each file has a name, which you create. Actually any character can be used except slash, but you have to do extra work to specify non-alphanumeric filenames, and you'll regret using one.
Many filenames end with an extension, i.e. a period and one to three letters.
Some programs such as web browsers depend on the extension to tell how to process the file. Files in the current directory are accessed just by their names. To specify a file in another directory give the name of that directory, slash, the filename. Please remove files that you're not going to use any more, particularly large ones. You may specify specific files or directories to be listed.