Q: How can I turned black screen off, so I can use the screensaver when I'm not using the computer?

Since I updated my iMac to Sierra, my screen goes black instead of going to my screensaver.  I can't remember how to remove this. I think it is going to sleep, but I would rather use the screensaver which allows me to know if the computer is on. Black screen makes me think it is off, and I don't wish to keep my computer on when I'm not using it unless it is temporary.