Pictures of the screen (screenshots) are saved as files on the desktop, but if you prefer to put a screenshot in the Clipboard, hold down the Control key while you press the other keys. You can then paste the picture into a document.

ActionShortcut
Take a picture of the whole screenCommand (⌘)-Shift-3
Take a picture of part of the screenCommand (⌘)-Shift-4, and then drag the crosshair pointer to select the area. Continue to press the mouse button, release the keys, and then press Shift, Option, or the Space bar while you drag to resize the selection area. When you are ready to take a picture, release the mouse button.To cancel, press Escape before you release the mouse button.
Take a picture of a window or the menu barCommand (⌘)-Shift-4, press the Space bar, move the camera pointer over the area to highlight it, and then click.To cancel, press Escape before you click.
Take a picture of a menu, including the titleClick the menu to display the menu commands, press Command (⌘)-Shift-4, and drag the crosshair pointer over the area.To cancel, press Escape before you click.
Take a picture of the menu without its titleClick the menu to display the menu commands, press Command (⌘)-Shift-4, press the Space Bar, move the camera pointer over the menu to highlight it, and then click.To cancel, press Escape before you click.