I don't know if this is the right place to post, but... My problem is really simple. I have two monitors: my laptop screen, and a TV linked through the HDMI port. I want to play VLC on the TV screen and still be able to work on my laptop so that my toddler can watch Totoro while I write. It used to just let me do this: I would drag the window from my laptop screen onto the TV screen and we were good to go. But suddenly, for no readily apparent reason, it started showing the same thing on both screens. I've tried installing kscreen and rebooting but I don't see any new tools that will actually allow me to manage multiple screens. Note that I'm totally an incompetent user with no programming skills. I know how to execute like five commands in a terminal. So keep it dumb.

no commands

in System Settings
under Hardware, you got Display and Monitors
you should see both screens there, you should be able to arrange them the way you want

- which is primary
- resolution of each
- which is left or right to the other, ( or up/down if you prefer )
- unify outputs is synonym for mirror, so you might want to disable that

cheers

I just tried plugin in my TV into my laptop for the first time. both are only a few months new.

Plasma automatically ask me what kind of settings I wanted

- single output
- mirror
- side by side

then I could go into system settings for more options

when I disconnected the external monitor though, plasma/kwin did not disabled that extended desktop
so I could still move my mouse to an invisible work area...

I had to disable the now unplugged screen from the settings

hope this helps