The FOIA allows you to request information from any U.S. government executive agency. Usually the heads of executive agencies are appointed by the President of the United States. Think, Department of State (DOS), Department of Justice (DOJ), Department of Health and Human Services (DHHS), Department of Veteran (the VA) Affairs, Federal Aviation Administration (FAA), etc. and also more obscure agencies like the Merit Systems Protection Board. Often these agencies are referred to by their acronyms. These also include the branches of the U.S. military, which are housed in the Department of Defense (DOD), such as the Army, Navy, and Special Forces, with the exception of the U.S. Coast Guard (USCG) which was moved to the Department of Homeland Security (DHS) when DHS was created after 9/11. These agencies within agencies are called components.
When you are thinking of what you want to FOIA, you want to learn a little bit about what part(s) of the U.S. federal government is in charge of your topic/subject of interest. You may want to do some research on the agencies themselves. It can be helpful to have a question that you want to answer. For example, if you see patterns of enforcement or concerning government official behavior and you want to know more about how and why certain policies are being enforced. You may have an interest about how certain policy decisions are being made—who is making them and why—in order to help you advocate or lobby for a change in the policy. You may be interested in how the government is structured, and what kind of information it produces, and get access to that information (i.e. demographic statistics, monitoring of the environment, public health data). You may have questions about things that happened in history, or that are happening and affecting your community right now.
Where do I submit my FOIA?
Some agencies are quite messy with multiple layers of components, like the DOD, the DOJ, and DHS, while others are very simple with no components, like the Department of State. It can be helpful to think of agencies as umbrellas, with the components underneath. For example, under the DOD umbrella is the Army, Navy, Special Operations Command, and the U.S. Southern Command, among MANY others. While you could send the request to the main DOD office (the Office of the Secretary of Defense), it would likely get re-routed to the relevant component, adding time, paper-work, and the chance that it will get lost. Some of the hardest work is figuring out which agency office will likely have the information you seek!