Press the Print Screen Key on your keyboard. It will seem as though nothing has happened until you open an image editing program (if you have no additional image editing software, you can use Microsoft Paint). Go to Edit and click Paste. Your desktop will appear in the editor. You can use the tools to crop or highlight the essential sections. Save the image to a folder or your desktop, type a name for the file, select the file type, and click Save. You can now send the screenshot.
Per Mac Command Key + Shift + 3 This combination takes a screenshot of your entire screen, saving it on your desktop as Screen shot "Year-Month-Day". You can then send this file wherever you want.
Command Key + Shift + 4 This combination allows you to use your mouse to take a screenshot of a specific part of your screen. After pressing the combination, go to the section of your screen you want to capture and hold down on the mouse. Drag the square over the section and release. The screenshot will appear on your desktop as ‘Screen shot "Year-Month-Day"’.