For God sent not his Son into the world to condemn the world; but that the world through him might be saved.
John 3:17 (KJV)
The Display dialog box shows the screen(s) connected to your system and allows you to graphically change settings like the resolution. Get to it from Menu –> Settings –> Display
In a multiple-screen environment; click and drag screen(s) to arrange them to match their physical location and use the slider to make one of them the primary display (where your menu and panel appears)
Click the Advanced tab to create display profiles. If / when you switch displays, display profiles will make the system immediately recognize previously connected screens / screen configurations.
More Information How to set a custom screen resolution in Ubuntu Desktop on TecMint, Config and Resolution on Ubuntu Help Wiki, Monitor Section of Xorg.conf, xfce4-settings – Display on Xfce 4.16 Documentation, Xorg on the Debian Wiki and Wayland at FreeDesktop.Org