One of my all time favorite utilities is Grab. It comes with OS X and it is free. It lets you quickly take pictures of all or part of your computer screen.
The really nice feature is Timed Screen. You can actually select a portion of your application that you want to point to, set the timer, and move your cursor to point to that specific item before the picture snaps.
I use Grab so often that I keep the icon for it on my Dock.
To use it, Open Grab (located in the Utilities folder which you should find in your Applications folder).
Choose a command from the Capture menu. (selection, Window, Screen, or Timed Screen).
Follow the directions for the task you have selected and save your finished product. This is a great tool for training and/or for asking questions.
One note, if you use Timed Screen you will get an image of your entire desk top. You may want to do a second Grab action and narrow your image to just the area you are interested in, as I did in the example above.