there is a person i don't know on my friends list on facebook, i am FREAKING out?

[Jack]

1. Remove the person from your friends list (preferrably full on block him)
2. Change your FB password.
3. Change the passwords on any other online accounts that happen to be the same as your FB password.
4. Warn everyone on your friends list that your account was compromised and to not trust any messages they received from you in the past week or so.
5. Going forward, always be very suspicious of any emails or other messages that claim to be from facebook. What most likely happened is that somebody sent you a fake email that sent you to a fake "login" page that sent your username/password to a spammer. Said spammer then logged in to your account and added himself so that he could spam your wall and send more of those fake messages to your friends in the hopes they he'll get their passwords too.