Firstly, does the record office have an online catalogue? If it does, search through it and familiarise yourself with the records that are held there.
Tip: Write a detailed list of what information you are looking for and prioritise it...I can guarantee you, time will fly and you probably won't get through your list! Make notes of sources you search and whether successful or unsuccessful.
Assuming US record offices work in the same way UK ones do, there will be some sort of paper/electronic catalogue system where you search for the reference number for the documents you require, then fill in a form quoting the reference numbers dates & details etc, and this is given to the person at the desk who will then get the actual documents (unless some are on a self-serve microfilm system).