What he didn't put in was the drive letter for the mount.
Shoot-em-upper, if you get the "USAGE" message, it means you entered the command incorrectly.
If you entered it right, you should get a message
Drive (letter) is mounted as local directory (path), where the letter and path are those you entered for MOUNT command to use. Look at this screenshot to see how it works:
And of course, there is always the
Beginner's Guide to walk you through the basics.