An annulment is a declaration by a Church tribunal (a Catholic church court) that a marriage thought to be valid according to Church law actually fell short of at least one of the essential elements required for a binding union. The United States Conference of Catholic Bishops have put together a very helpful lists of FAQs, you can find that list here.
If you need help seeking an annulment, you should begin with your parish priest. If for some reason you do not have a parish priest, one of the priests at the Cathedral would be happy to sit down with you and discuss the process. If it is determined that you should be seeking an annulment, you will then be referred to a procurator, someone who is qualified, and has the time, to take on your case.
Please call the Parish Office if you need to talk to someone.