Marriage certificate courthouse?

I am getting married at the courthouse Wednesday March 10 2010. Do you have to have a marriage certificate first or do you get it after you are married? And can we wear our rings before we get married say on the way to the court house because my ring is a little small going over my knuckle it will go on it will just take a minute and i dont want there to be any awkard silence during the exchange of rings at the courthouse