Sharing and privacy
Even if you customize your privacy settings, it's important to understand that the things you share on Facebook are visible to a lot of other people. This is because Facebook is designed to be more open and social than traditional communication tools.
For example, let's suppose you post a photo on a friend's Timeline. By default, that photo will be visible to all of your friends on Facebook, not just the person you shared it with. The photo will also be visible to anyone who is friends with your friend. This is one reason people enjoy using Facebook—it's easy to share with lots of people at the same time.
As long as you're somewhat careful about the things you share, Facebook doesn't pose a serious risk to your privacy. Before you share anything on Facebook, such as a comment or a status update, you'll need to consider how comfortable you are with many people seeing that information. If you wouldn't feel comfortable sharing something in a public place, you may not want to share it on Facebook either.