The cinnamon sticks or quills are the dried bark of a tree. There are two popular varieties of cinnamon; from Chin and from Ceylon. They both have similar flavors but the cinnamon from Ceylon has a sweeter aroma and is found more as sticks than a rolled up quill. The Ceylonese cinnamon is also not so easily available in local markets.
Cinnamon (and mostly the Ceylonese variety) in its stick/quill for as well as powdered, is used extensively in Indian cooking, mostly for savory dishes. Often times a few bits of broken sticks are added as the oil heats up; this way the oil is flavored and the food is cooked in this fragrant oil. Sometimes it is dry roasted in a skillet before cooking, which intensifies the aroma.
The warm sweet flavors make it a popular spice for desserts in the western world, especially during the holidays.
It is one of the ingredients of Garam Masala.