Pubic lice are just that, lice that has infested your public hair. The most common symptom is intense itching, usually felt mostly at night. Some victims have no symptoms, others may develop an allergic rash.
Various shampoos and lotions exist to kill lice, but the best solution is simply to shave off the pubic and hair and shower vigorously afterwards.
Nominally through sexual contact, however they may be picked up through use of sheets, towels or clothing used by an infected person. This may also occur due to lack of hygiene in terms of daily bathing etc.