Using "terminal"
This is the long winded way.
Change directory to where the ISO image is located
cd /Volumes
ls -al - to find what volumes are mounted, i.e too see where you uwant to go next
cd VOLUME_NAME
(This is the same as cd /Volumes/VOLUME_NAME)
ls -al - to check the files are there in the ISO image
cp -R * $HOME/Desktop/.
This will copy the files from the "mounted" ISO image to the desktop in your MacOSX account.
If there are a lot of files and subdirectories, it will be worth creating a new foler on your desktop - say TEMP, you can do this from MacOSX GUI.
Then the command line would look like
cp -R * $HOME/Desktop/TEMP/.
NOTE: $HOME - is a UNIX environment variable, this is set to the home directory of the currently logged in user.
NOTE: The "Usage" line that got returned just means there was something wrong with what got typed.