i didn't know the answer to this so i searched the world wide web.
I took a human sexuallity class earlier in the year of 2009 and this website helps with alot of unanswered questions.
here is the link.
Human Papilloma virus (HPV) | What Are They? | Sexually Transmitted Infections | Teens | sexualityandu.ca - Your Link to Sexual Well-Being
hope this help.
and for the record, the local health unit uses this site to help teens understand sex topics so it is real and ligit. not just some random site