On a PC
Press the "PrtScn" key, and a screenshot of your computer display will be automatically copied to the clipboard. You can then open an email or click "Reply" to an existing email and use CTRL+V to paste the image into the body of your email. If that does not work, you can open a program that handles pictures, like Paint or Word, and paste the image into the document.
Note: On some laptops, it may be necessary to press the “Alt + Fn + PrtScn” keys instead. Check your laptop’s manual for more information.
On a Mac
Hold Shift + Command + 4 and you will see "crosshairs" - drag these around the item you want to take a screenshot of and this will be saved automatically on your desktop. Attach this to your email.