How to Take Screenshots
From Legacy Roblox Wiki
NOTE: This article expects you to have a keyboard with "PrtScr" or something similar (e.g. PrintScreen, PS, etc.)
When you press the "PrtScr" button, what you see on screen will get copied to your computer's memory, also known as "the clipboard". Open any picture-editing software, (such as MSpaint), and "Paste" the picture by pressing Ctrl+V. Now you can save the picture, or edit it however you want.