If you are using Windows 10, 11 you can use the shortcut Windows Key+PrtSc.
This will make a screenshot, and save it in your C:/Users/Username/Pictures/Screenshots folder.
If you wish to make a screenshot of a specific area: you can use the shortcut Windows key+Shift+S. It will pull up the selection area. Left click on your screen and while holding left click, drag the mouse to designate the area. Once you've done it, you can paste with shortcut ctrl+V your screenshot.
If you wish to save it, click on your Action Centre(the icon to the right of the clock as in the screenshot below)
Then, click on 'Snip & Sketch'.
In this appeared window, click on 'Save' icon.
For macOS:
If you want to make a screenshot of the main display, use the shortcut cmd+Shift+3, and it will screenshot whole area, and place this screenshot on your desktop.
If you want to take a screenshot only of the specific part of the screen, consider using shortcut command cmd+Shift+4.
Once you've used this shortcut command, click on the screen and while holding click, move the cursor to designate the area. Once you've done it - your screenshot will appear on the bottom right side of the screen, and then automatically to Desktop.
This will appear once you release the click after selecting an area:
You can click on this - and it will pull up menu to edit it. Once you've finished - click 'Done'. and the screenshot will appear on your desktop.
If you are using the version of the OS which does not have snipping tool built-in, for example Windows 7, 8, you can click PrtSc button on your keyboard, then either ctrl+v it to the message, or open Paint application.
Click ctrl+V in your Paint application, and go to File->Save As. After this was done - your screenshot will be saved and you can send it.