Screenshot is copy of your full screen, little selecion or only from one window with a trouble. It’s very useful to share your experience or show your problem to someone.
Another method is to work with this cheat sheet:
Command-Shift-3: Take a screenshot of the full screen, and save it as a PNG-file on your desktop
Command-Shift-4: select an area: Take a screenshot of an area and save it on the desktop
Command-Shift-4 + space: select a window: Take a screenshot of a window and save on the desktop
Command-Control-Shift-3 take a screenshot of the screen, and save it to the clipboard
Command-Control-Shift-4 select an area: Take a screenshot of an area and save it to the clipboard
Command-Control-Shift-4 + space click on a window to select it: Take a screenshot of a window and save it to the clipboard.
As you see 11111 this post takes some time in the draft area before it was published