Below are the keyboard combinations that you can use to take a screenshot on a Mac;
Command-Shift-3 – This takes a screenshot of the entire screen and saves it to your desktop.
Command-Shift-4, then select an area – This takes a screenshot of the selected area and saves it to your desktop.
Command-Shift-4, then space and then click a window – This takes a screenshot of a window and saves it to your desktop.