There's a hold on my enrollment. What do I do?
That depends on your hold, actually. Most holds result from unpaid fines, like parking tickets or library overdue charges. The way to clear those is by paying off that department. Some schools will place a hold on enrollment until you receive advising or some other kind of approval, in which case you'll just have to go through that process first.
When you go through the Enroll & Pay system, log in, and on the home screen click "Holds and To-Dos". It will tell you who has put the hold on the account, and where to have it cleared.