Open a command (MS-DOS) prompt locally or remotely.

FTP-connect to your server, e.g. ftp 127.0.0.1
Log in.

Type dir and hit return. you should see the directories courses and testfiles.

Change directories to the courses directory by typing cd courses. Try creating a subdirectory by typing mkdir test1. If you succeed, change directories to the testfiles directory and try creating a new directory there:
cd ../testfiles
mkdir test1

If you get an "Access Denied" error, you need to enable write privileges to the directory and its children. Authors will be unable to upload files to these directories unless these tests pass!