Here they are, plain & simple!
- Command-Shift-3: Take a screenshot of the screen, and save it as a file on the desktop
- Command-Shift-4, then select an area: Take a screenshot of an area and save it as a file on the desktop
- Command-Shift-4, then space, then click a window: Take a screenshot of a window and save it as a file on the desktop
- Command-Control-Shift-3: Take a screenshot of the screen, and save it to the clipboard
- Command-Control-Shift-4, then select an area: Take a screenshot of an area and save it to the clipboard
- Command-Control-Shift-4, then space, then click a window: Take a screenshot of a window and save it to the clipboard