If you want to take a screenshot on your Mac, you need to know the keyboard shortcuts to do it (or have an app).
- Command – Shift – 3: Take a screenshot of the whole screen and save it as a file on the desktop.
- Command – Shift – 4: Use this shortcut to select an area (with the left mouse button). After the selection, the screenshot will also be saved on the desktop as a file (PNG).
If you want to save the screenshot to the clipboard instead of a file, also press the Control key (Control – Command – Shift – 3 or Control – Command – Shift – 4).
Here is the link to the official support document.