Personally, I had never used the U.S. National Archives databases until a few years ago, when I started using the Numident Files, which are fantastic resources. I have discovered a wealth of documents, indexes, and a search capability that you can get lost in!
A great place to start is to review the Genealogy Research Topics that you are interested in. There will be indexes and databases specified that you can search or browse. Here is the list with the links:
(Updated November 2023)
- African-American Research
- Aliens
- Bankruptcy Case Files
- Caring for your Family Archives
- Census Records (1790-1940)
- Chinese Immigration
- Citing records in the National Archives of the United States
- Congressional Records: Private Claims and Private Legislation
- Court Records
- Electronic Records for Genealogy or Other Personal Research
- Ethnic Heritage Research and Resources
- Exploration and American Expansion
- Federal Employees
- Immigration Records
- Income Tax Records of the Civil War Years
- Internal Migration
- Japanese Americans
- Land Records
- Maps of interest to Genealogists
- Maritime
- Microfilmed Records
- Military Records
- Native American Records
- Naturalization Records
- Naval Records
- Passenger Lists
- Passport Applications
- Post Office Records
- Pre-Federal Records
- Prisons
- Social Security Records
- State Department Records of Genealogical Interest
- Tax Records
- Vital Records
- Women
I would also recommend that you read the National Archives Catalog Guide for Genealogists and Family Historians
You will find many databases above in the list of Resource Topics. There is an important page that you should then peruse. It is Access to Archival Databases There are several links that help you to find online databases and indexes. I will repeat the links here:
Time Spans
Finally, the Numerical Identification Files (NUMIDENT) files from the Social Security Administration have three types of files: 25 million life or death claims; about 50 million death files; and 72 million SS-5 Application files. All span 1936-2007.
Don’t miss these resources. They are abundant and I’m sure that they will grow in the coming years.