You can select from a variety
of sources for your screen capture, including Full Screen, any window or
icon, a rectangular selection, or a movie sequence. Once you select the
source button you will see the "marching ants" highlight of what you will
actually capture. Hit the Enter key to capture. Your captured image
will open in Finder, allowing you to save and/or print.
With Grab opened and running
you can select from a choice of capture formats, depending on which part
of a screen to want to capture.
Grab saves in a .tiff format.
You can open the captured file in Preview and save as a .png or jpg file
if necessary. You will be printing out a screen capture in an upcoming
project, so become familiar with both applications.