A second display can act as either:
- a mirror of the first display.
- a bigger desktop area.
You may be able to connect your Mac to one or more external displays, depending on the technical specifications of your device.
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When it's mirrored, the same thing appears on both screens. Your interactions appear on both screens, identically.
When it's a bigger desktop, it works the same as if you had a single display with a larger area. You drag things around just as you normally would, there's just more space to do it in.
For example, if the 2nd display was to the right of the builtin display, and you positioned a window so it was half-way off the right edge of the builtin display, then the "off-screen" part of the window would be visible on the 2nd display. In short, you effectively have more display area.
You control the cursor the same way you would if you had a single big screen. That is, the cursor moves around as usual, you click things to select them, and you type into the thing that's in front. If you're filling in data in one window (regardless of which screen it's on), then keyboard focus is in that window. There are limited mouse interactions with other windows (also regardless of screen), mainly scrolling or dragging the window around. Those are done by holding down the ⌘ key and then clicking the window-title or the scroll bar (or use another configured Gesture). If you omit the ⌘ key, then the click will bring the window to front, and you'll lose the keyboard focus in the other window. This works exactly the same regardless of the number of displays. It comes down to how windows work, not anything to do with displays.
Oh, and you can setup spaces to correspond to displays.
On your Mac, if the desktop becomes cluttered with open app windows, use Spaces to organize the windows into additional desktops.
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