How to Use Mac OS X Grab to Save Screenshots
Grab is an image capturing application that comes preinstalled on every Mac computer. The application allows you to capture a selected portion of the screen, a selected window or the entire screen. You can find the Grab application in the "Utilities" folder and use it to save a selected screen shot.
Click the "Finder" icon in the computer's dock, followed by the "Applications" folder icon.
Click the "Utilities" folder icon and double-click the "Grab" application icon to launch it.
Click the "Capture" tab and select the "Screen" option from the Capture menu. The captured screen shot will now appear in the Grab window.
Click the "File" tab and select the "Save" option from the File menu.
Type a name for the screen shot in the space provided and click the "Save" button to save it.