Marriage records online are usually indexed according to country, state and county, depending on where the marriage took place. It is worth bearing in mind that some couples may have been married in a location away from their home town or county. Some data bases will contain images of the actual marriage certificate while others have indexed the relevant information. When searching for a particular marriage certificate you would need to know whether records are available for the dates when you would have expected your ancestors to be getting married, and whether or not the marriage database is complete. When you find a record in a marriage index, you can follow it up byrequesting the original record, and the location where the records are held.