The letter says you can work for 90 days under the guidance of an already licensed RN. Once you send in your application (bottom half of the pass letter) with your check, your number should be posted on the IDFPR website in about a week. You'll get the license in the mail about a week after it's posted online.
My facility would not let me work with the pass letter. But once they were able to see the number online I was fine.