Administrative agencies are primarily concerned with rulemaking and adjudication. Rulemaking is discussed on the page "Regulations and Interpretive Rules." Adjudication is an agency decision regarding permitting, licensing, or enforcement of rules and regulations. Adjudicators may be administrative law judges and are not Article III judges - meaning they are a part of the legislative process and not the judicial branch. Agency adjudicators are civil service employees that are not appointed for life and subject to impeachment.
USCIS - United States Citizenship and Immigration Services
AAO - Administrative Appeals Office
BIA - Board of Immigration Appeals
OCIJ - Office of the Chief Immigration Judge (immigration court)
OCAHO - Office of the Chief Administrative Hearing Officer
ICE - Immigration and Customs Enforcement
CBP - Customs and Border Protection
Administrative decisions are often released on agency websites and available on legal subscription databases like Westlaw, Lexis Advance, and Bloomberg Law. These decisions may also be published in reporters like judicial decisions. See Table 1 in the Bluebook - it lists federal entities and where some of the materials are published. Note that the Bluebook is not comprehensive and may not reflect up-to-date or easy to use electronic information.
IMPORTANT: Not all administrative decisions will be precedent decisions - this means they do not have precedential effect for future adjudications and should not be solely relied on for relief. A non-precedent decision is binding only on the parties involved.
As with other information published on agency websites, it would benefit you to become familiar with these websites to see what is and is not available. A good resource for finding administrative decisions online for many agencies is the guide "Administrative Decisions" from the University of Virginia.