iMacs and MacBooks don’t come with a straightforward Print Screen key, however there are keyboard shortcuts that help you to get the screenshot you need. These shortcuts are fairly quick and easy to learn.
Capture The Entire Screen
Option 1: Hold down the Command + Shift + 3 keyboard keys simultaneously to instantly capture your desktop screen.
Option 2: Hold down the Command + Shift + 3 + Control keyboard keys simultaneously to save the image to your clipboard.
Capture A Section Of The Screen
Option 1: Hold down the Command + Shift + 4 keyboard keys simultaneously. Your mouse cursor will then turn into a crosshair. You can now click and drag to draw a box around the area you would like to capture. Let go of the mouse button to capture, the screenshot saves to your desktop.
Option 2: Hold down the Command + Shift + 4 + Control keyboard keys simultaneously and follow the instructions above. When you let go of the mouse button to capture, the screenshot will save to the clipboard.
Capture A Single Window
Option 1: Hold down the Command + Shift + 4 keyboard keys simultaneously so that your mouse cursor becomes a crosshair. Then press the Spacebar to change the mouse cursor to a camera icon and the screen turns light blue. The window you hover over is highlighted with a light blue overlay. Simply click on the window you would like to screenshot and the image will save to your desktop.
Option 2: Hold down the Command + Shift + 4 + Control keyboard keys simultaneously so that your mouse cursor becomes a crosshair and follow the instructions above. When you click on the window you would like to screenshot, the image will save to your clipboard.
Use The On-screen Marquee
Option 1: Hold down the Command + Shift + 5 keyboard keys simultaneously to choose full screen, a specific window, or a defined portion. It will then save the screenshot to the desktop or another location.
Option 2: Hold down the Command + Shift + 5 + Control keyboard keys simultaneously and follow the instructions above. It will then save the screenshot to your clipboard.
Source: Mashable
