Let's say you want to make sure you can write to a directory you created.
1. select * from dba_directories where directory_path = '/usr/tmp';
2. In my case, I had three. I decided to test the ODPDIR directory.
l_file := utl_file.fopen( 'ODPDIR', 'ODPDIR.txt', 'W' );
utl_file.put_line( l_file, 'Here is some text' );
utl_file.fclose( l_file );
4. I ssh into my server, cd to /usr/tmp, and I see a file called ODPDIR.txt has been created. Whoot!