This will bring a crosshair pointer that you can drag to select the part of the screen you want to capture. If you don't want to capture your entire screen, you can press and hold Shift + Command + 4 keys together. If you don't want to edit it, you can wait for the screenshot to save to your desktop. Click on the preview of the screenshot to edit it.A thumbnail will now appear in the corner of your screen to confirm that a screenshot has been captured.Press Shift + Command + 3 together to take a screenshot of the entire screen.