If it is an image from a web page that you want to capture, you can simply drag it to your desktop, your document, or your email. But if you want to capture an application’s window, the Apple Dock, or a menu the PRTSC key always came in handy on a Windows machine.
Luckily, on a Mac you have a much more flexible and powerful screen capture utility.
Command-Shift-3: takes a picture of the whole screen.
Command-Shift-4: takes a picture of part of the screen, press then drag to select the area you want in the picture.
Screen shots are saved as files on the desktop and are named “Picture 1”, “Picture 2”, etc…
To place the screen shot in the Clipboard instead of saving it to a file, hold down the Control key when you press the other keys. For example, Control-Shift-Command-3 to copy the whole screen to the clipboard. You can then paste the picture into a document or email via Command-V.
Also make sure to check an Apple utility called Grab, found in your /Applications/Utilities folder.