If you just need a shot for immediate copy-and-paste purposes—not something you want to save to your desktop—add the Control button into the mix. For screenshot of the entire screen, you’ll press Command + Shift + Control and then 3. This will copy the screenshot to your clipboard instead of saving it to your desktop. When you’re ready to paste it, hit Command + V.
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You can also take screenshots through the Preview Application. Open Preview, and from the File dropdown menu, hover over Take Screenshot. From there choose to capture a screenshot of a Selection, Window, or Entire Screen. Once it’s been taken, the image appears in preview. With Preview, you can change the automatic PNG format to JPEG, PDF and more.