what can i do with facebook now that i signed up?

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I know this is going to sound like i'm not from planet earth, but what i have no idea what i can do on facebook beyond looking for people i already know and sending them a friend request. Do people only invite people they know as friends, or do they invite anyone that looks interesting? When you submit a message to facebook does everyone see it, or only your friends? Lastly, how do you put your business on facebook? Thanks for helping.