1. Chakras are energy vortices in your body, basic systems use 7 major ones but working with them deeper allows you discover many other chakras.
2. You meditate upon them and cleanse them. All chakras are open to a certain degree, depends on the individual.
3. You basically re-align your energy flow and move to a more balanced state once they are working properly
Of course this is just a basic overview, its best to google and find out as much on them as possible :)