Bell's palsy is a paralysis of the facial muscles (either the left or the right side). The facial nerve exits the skull base through a small opening near the back of your ear (mastoid region). If the nerve swells for whatever reason, the nerve will stop working and you get half your facial muscles paralyzed.
Treatment consist of medications like steroids to reduce swelling and anti-virals as herpes zoster infection is one of the common cause of Bell's palsy. Some doctors will provide vitamins for the nerve (neurobion for instance).