Brunoise are used in sauces, soups, as a garnish, or sometimes simply as a way of hazing culinary students. Out in the wild, however, every head chef has his or her own particular (not to say "peculiar") set of definitions for various culinary terms and procedures. So one chef's brunoise may be another chef's small dice.
Feel like practicing your knife skills? Here's an overview of the basic knife cuts. Plus, this article on Knife Skills 101 covers everything from how to hold a chef's knife to how to sharpen it.