All of the FDLP materials are classified in the Superintendent of Documents call number system. For more information on the Superintendent Classification System, please see the GPO Classification Manual.
1. The Government Publishing Office
The Government Publishing Office (GPO) was established as the Government Printing Office in 1861 and has been the official distributor of government documents ever since. The GPO website is a great starting point in the research process as it leads to other good sources of information such as: GovInfo, Ben's Guide to the U.S. Government, and the Catalog of U.S. Government Publications.
2. DiscoverGov
DiscoverGov is the newest of all the sources on this list. DiscoverGov in useful for searching multiple government databases at the same time. For example, instead of searching the Catalog of U.S. Government Publications and GovInfo separately, simply search DiscoverGov. The only caveat is that there is minimal browsing available so you will need to know what you are looking for specifically.
3. GovInfo
GovInfo is the successor to the Federal Digital System (FDsys). GovInfo is a system created by GPO for the purposes of accessing government documents that are produced by all three branches of government. As such, this resource is a great for searching primary sources of law like, the Congressional Record, the Code of Federal Regulations, the Federal Register and the United States Code. This is a good database if you are not sure what you are looking for as there is a lot to browse.
4. Ben's Guide to the U.S. Government
While Ben's Guide contains material designed for children, in truth, all ages are welcome to explore Ben's Guide. If you are looking to learn more about the general history and structure of the United States government, in a way made fun, then Ben's Guide is a great starting point.