When you view the contents of a directory you can see all the files that exist in that directory because the operating system or application that you are using displays a list of filenames. You can think of these filenames as links that join the files to the directory you are currently viewing. If you unlink a file, you are effectively causing the system to forget about it or delete it! Before you can delete (unlink) a file, you must first be sure that it is not open in your program. Use the fclose function to close down an open file.
PHP – Unlink Function
<?php $myFile = "testFile.txt"; unlink($myFile); ?>
In this case file named as testFile.txt will be deleted which is in the same directory as unlink script file is.