Taking a screenshot on a Mac is slightly different than taking one on a PC. To capture the entire screen on a Mac, simultaneously press Command, Shift and 3. The image immediately appears as a .png file on the desktop.
This method of taking a screenshot is most similar to using the Print Screen button on a PC. To capture only a specific portion of the screen on a Mac, simultaneously press Command, Shift and 4. Move the crosshair near the corner of the desired screenshot area. Hold down the left-click button, and drag the box over the intended portion. Release the left-click button to generate the screenshot.