I want to use a second monitor. A search revealed that by default a second monitor is added as clone. In my case, however, it's added as extension. Where/how can I set this to have a second monitor showing exactly what the primary monitor shows?
Thx for the help. I followed your advice, was able to open arandr but I couldn't find an option to mirror the screens. I can set the resolution of both screens, I can select one of them as primary, in the GUI I can move the screens on the canvas to left and right to adapt the layout to the real world situation but I couldn't find an option to mirror the screens.