At the end of your registration interview, you were probably given a list of port of entries. You have to leave the country from one of these ports. On the day of your departure, you go to the airport (or border post), talk to the immigration officer. They will take your I94 from the passport. Make sure that you leave the country on the same day. If they take your I94 and you don't leave for some reason, you are in trouble.
When you come back, you have to re-register.
I think this answers your question.
Good luck.