Friendship Books are passed between friends. That means that once you receive them from a friend, you need to place your address (I suggest once again to use address labels) and then share a bit of information about yourself - such as likes or hobbies. For example, I like to write down after my address that I love myths, legends, chocolate and ice-cream! Once you are done with that "filling the FB" part, you can flip through its pages and see if there is an address that you might be interested to write to. If not, then you are ready to pass the FB to another penpal of yours.
Things that you should know:
1) Never pass FB's to a person whose address is already inside. There is no point of repeating the addresses, right?
2) When the FB is full (there is no place for anyone else to sign) please be honest and send it home to the owner of the FB or to any ICR (I can return).
3) Pass the FB's as quickly as you can - usually they take years to get filled, so don't leave them hanging around for too long.
4) Don't ad pages to FBs so you don't have to send the FB home. Don't remove pages either!