How to Take Screenshots
From Legacy Roblox Wiki
Since ROBLOX can only run on Windows, this tutorial is intended for Windows users.
Most non-Macs have a button called "Print Screen" on their keyboard that says "PrtSc" (meaning "print screen").
When you press this button, what you see on screen will get copied to computer's memory, also known as "the clipboard". Now, open any picture-editing software, (such as mspaint), and "Paste" the picture you have stored in the computer's memory by pressing Ctrl+V. Now you can save the picture, or edit it however you want.