Here are the steps to take a screenshot on your Mac computer:

1. To take a screenshot of the entire screen, press and hold these three keys together: Shift, Command, and 3.
2. If you see a thumbnail in the corner of your screen, click it to edit the screenshot. Or wait for the screenshot to save to your desktop.
3. To take a screenshot of a specific part of your screen, press and hold these three keys together: Shift, Command, and 4. Then drag the crosshair pointer to select the area you want to capture.
4. If you want to capture a window or menu, press and hold these four keys together: Shift, Command, 4, and Space bar. The pointer changes to a camera icon. Then click the window or menu to capture it.