Are you losing track of who your character knows and how? You could write it here, and always have it to look at. Heck, we could get enough information to create a crazy character web. Maybe as crazy ridiculous as the
Character relations map from the Count of Monte Cristo, though that's a tough one to beat.
Also, if you want to start interacting with a character but don't know how, you can always PM the player you wish to play with, or post here what you would like...
Use it wisely!
Edit: if you don't have a specific plan, use this place to tell us a little about your character, some of the things that might not belong in the Character description itself... stuff that would help us figure out why and how our characters know each other.