Being placed on a waitlist does not mean you are in the class and does not mean you will get into the class. Every department has a different procedure when it comes to waitlists so depending on what course you are waitlisted for will determine which department oversees the course you are waitlisted for. If you are able to get off the waitlist and into the course then the department coordinator will send you an email. You will likely only have 24 hours to respond so make sure you are checking your email. The following link is a list of each department and their waitlist procedure.
It is best to find yourself another course just in case you are not able to register for the course you have on your waitlist!