How to chiffonade:

This is a cutting technique that can be used on any flat, leafy food (such as spinach, basil, and mint). It quickly creates uniform, elegant curls. 

Stack the leaves of your herb or green (pictured above: mint) and roll them together tightly. Place on a cutting board, and with a sharp knife cut across the rolled leaves to produce fine ribbons. Separate ribbons and use as desired.

To see a demonstration of the technique, go to 4:55 in this video.