This video will help orient you to the process of researching at the National Archives:
More basic information about researching at the National Archives can be found here: https://www.archives.gov/dc/researcher-info
Before starting your research, please ensure that you have read up on the rules for the National Archives. This can be a daunting task as there are many!
Some that I'd like to highlight for you:
The most extensive list of rules can be found here: https://www.archives.gov/research/research-room-rules
From the National Archives website:
The National Archives Building in Washington, DC (Archives 1), houses historical records of all three branches of the U.S. Government (Executive, Legislative, and Judicial). Our holdings include:
An additional overview of textual records found at the National Archives can be found here: https://www.archives.gov/dc/research/textual-records
I highly recommend searching the Guide to Federal Records in the National Archives of the United States to get a better sense of the kinds of things you will find within the National Archives. While it is not fully updated to reflect what you will actually find in the NARA catalog, it will greatly help to grasp what you might find.
To do this:
For example, if you search for "Korean War," you will be led to the General Record of the Department of State. Should you review the records locations, you will find that they are mainly found within the Archives 2 Building in College Park, MD.
Browsing the various Executive Agencies might also be helpful in leading you to topics of interest.
Consider also looking at History Hub, which is a community supported by the National Archives to crowdsource research requests and findings within the National Archives.
Once you've found something of note (or many somethings), make sure to reach out to the reference staff so that they can get your resources for you, as well as assist you in finding other items of interest. To email them, you want to reach out to archives1reference@nara.gov.
Here are things that you should include in the email:
Ensure that you place your request one week in advance, minimum.