The last combination that you can use with vector shapes is a "Crop."  Crop uses the top object in your stacking order to cut out material from every object beneath it.  Anything inside the top object is cut out and anything outside it is removed.  For this example we have placed the star on top of two circles and used it to crop them.

(Figure 10.7 (a) The star sits on top of the circles) 

 
(Figure 10.7 (b) The star used to crop the circles)

You can use the combination options in many different ways and come up with any number of different results.  Try experimenting with different shapes and see what you can come up with.

(Figure 10.8 Various combine settings with three shapes)