Hi Lisa S and welcome to our community
Basically I would set it up as multiple slides. On the first
slide, have four click box objects. One on each corner. Click a
click box and it jumps to a different slide with all shaded except
the one you clicked. Then perhaps a button that links back to the
original unshaded image.
Basically, you may "draw" rectangles using Highlight Boxes.
Or, you could draw other shapes using something like Microsoft
Paint or Fireworks, then import them into your project.
Cheers... Rick