I did not major in history as an undergrad, and did not write a thesis on a historical topic, so the first time I ever set foot in an archive was in my second semester of graduate school. This condition--being a graduate student in history that didn't know how to use an archive--had me breathing into a brown paper bag. The first year of graduate school is a nine-month grinding down of your confidence (see: impostor syndrome), and the specter of being berated by an archivist for knowing absolutely nothing was like twisting the knife into the heart of my fragile emotional being. It worked out well for me, though, because I decided that the best way to cope with my anxiety was to first go to a little archive with a nice archivist, get my feet wet there, and then face the big scary Manuscript Room of the New York Public Library the following day. In that little archive with that nice archivist, I found a wonderful collection of documents that inspired my whole dissertation! So, no regrets.
Now, three years later, when I go to visit an archive I feel excitement rather than anxiety. By the time I show up, I already know what I'm looking for--and more importantly, where to look for it. That's because I use archival finding aids to figure out what libraries have collections of documents related to the history I am researching.
What exactly is a finding aid? Well, let's say that a Very Important Woman (maybe a socialite? maybe a radical labor activist?) decided to donate all of her letters, diaries, business records, scrapbooks, and files so that future scholars can learn about her interesting life. She contacts a library she really likes--maybe her alma mater, or maybe a library to which her friends or fellow activists donated their papers--and they agree to preserve her documents for the use of researchers. When the library gets the Very Important Woman's stuff, it's probably in some cardboard boxes. Perhaps they're neatly placed in the same order they were in when they lived in the Very Important Woman's filing cabinet. Or, more likely, they arrive disorganized. An archivist then has to process this collection of documents. Processing means to put the records in an order that makes sense, whether it was the way that the Very Important Woman arranged them, or by placing them in order chronologically by year or thematically by topic (debutante balls and charity dinners, or union rallies and Communist Party meetings). As this order is created, the documents are placed into file folders and then into boxes (like this or this). Some collections fill only one box, but most take up several. Once everything is filed away, archivists create a finding aid; it's a map that tells you, the researcher, what documents are in those boxes and folders.
Before breaking down the collection into this level of detail, a finding aid begins with a description of the collection. If the collection is of an individual's personal papers, the archivists will also include an autobiographical note.
The beginning of a good finding aid will also list the subjects (topics or individuals or locations) that are especially prevalent in the collection.
After all of this, the archivists describes the contents of each box and folder. Finding aids are rendered in various degrees of detail, which can be challenging. If an archivist was given a substantial amount of time to process a collection, they usually include more detail about what's in each individual folder. Usually, though, a finding aid only tells you the label of the folder. It might say something like "Very Important Woman's Correspondence with Labor Activist," or "Debutante Balls, 1918-1919." As a researcher, you don't know if there's one letter or one hundred letters in that folder, or if "Debutante Balls" refers to parties thrown by the Very Important Woman or parties she attended. When you open that folder, you have no idea if you're in for some fun or some frustration.
So, how do you find a finding aid? Sometimes it's as simple as Googling "Very Important Woman." More often I use a database called Worldcat to search through many library catalogs at once. It can be unreliable because each library has to sync their catalogs up with Worldcat; if they do not, you might miss something. To be thorough, I also search the catalogs of libraries and archives that would be a logical place for my historical subject (either an individual or institution) to deposit their records. I look at all the public and university libraries in their city, or I look at special archives dedicated to a defining characteristic of my historical subject (like at an archive that specializes in American Jewish history or one that collects materials from social welfare institutions). It's time consuming to go to each library's website and type your search terms into their catalogs, but sometimes you find complementary collections to the one your were looking for. That's always a nice surprise!
Once I find my finding aids, I then decide if a collection seems valuable enough to justify a visit to that archive. Sometimes it's an easy decision, like when a library has the complete papers of the Very Important Woman who is the subject of your dissertation. Other times, you know you want to write a chapter about the Very Important Woman's favorite charity, and you look at the finding aid for their records--which with your luck are at an archive on the other side of the country--and you realize that the charity only donated one box of documents and all of the folders are labeled "Tax Forms" and dated from the 1970s, well after the Very Important Woman died. It's not worth buying a plane ticket to look at that! That's when you decide to cut the chapter, or to base it on research that has already been done (secondary sources).
Finding Aids are an invaluable tool to a researcher, but like all tools they vary wildly in quality and helpfulness.* Sometimes you end up with a top-of-the-line power circular saw with laser precision guide and built-in level, and sometimes you end up with this. The more you use finding aids, the more adept you become at working with what you're given!
If you're interested in looking at a few examples, here are a few finding aids from my own research that represent the spectrum of detailedness:
Solender Family Papers (American Jewish Historical Society/Center for Jewish History)
Fort Washington Branch Records (New York Public Library Archives)
Henrietta Scherer Papers (Tamiment Library, New York University)
*Let me make it clear that this is not always the archivists' fault. They are often underfunded and overworked. Most archives have more collections than their existing staff is able to process, but grants to hire more helping hands are really competitive and hard to come by. I love archivists and librarians, and could not do my job without them.