I need to know how to go about marring my fiancé while he is in jail and I now I need a marriage certificate first but I don't know how to do that. Anyone know how I would do that?

Without knowing where you are no one can give you specific advice.

Call the jail and ask about the procedure.

Is he in Jail or prison, it makes a difference. Many jails I know of will not allow it. So your first call should be the jail to see what the rules are