This is what happens when people don't elaborate pjg and by the looks of things, you actually turned off your laptop knowing it would to see if it would turn off your monitor might suggest you need a few lessons in understanding a computer.
Anyway to turn off your monitor it is done via screen saver power options. There you will have an option to turn off the display at a certain time.
Also you're able to change what closing the laptop lid does, either powering down monitor, shutting down laptop or do nothing.