The 7 major physical chakras are located along the midline of the body. Each chakra has an associated color and an associated symbol. It is through these 7 areas that Prana or Life Force or Chi energy flow. An imbalance in the energy flow or blockage in one or more chakras can be either a cause or symptom of imbalance in the body.
The following videos provide a very good description of the 7 chakras. You may also want to view this entry on Wikipedia.
Journey Through The Chakras Part 1
Journey Through The Chakras Part 2
Journey Through The Chakras Part 3