Screen curtain

[Gary]

Hi everyone.
I got my first MAC and love it.  I heard that there's a command to  
temporarily turn off the screen for people that want to practice with  
the VO commands.  I'm partially blind and  need to start turning of my  
monitor, but can't find the command to do so.  I don't want to use the  
dim screen commands because I would like to toggle to the screen on  
occasion.  Can anyone help?

Thanks,
Gary