To be a little more detailed, PC families are how you think of a member as a friend. Like, for example, if you think of... I dunno (Insert name here) as like a big-brother figure, and you've been friends for a long time (had to insert that because of all the n00bs out there; it should be common sense), then you can send them a PM asking to add them to your PC Family as whatever relationship, be it brother/sister, uncle, or whatever....