Congress passes laws that addresses a particular need. However, after the law is passed, the appropriate Federal agency creates rules that carry out the law. These regulations at the Federal level can be found in the Code of Federal Regulations (CFR). Individual states also have their versions of the CFR. For example, the State of Texas has the Texas Administrative Code (TAC) where you can find regulations from Texas state agencies.
To search specifically for government documents, use the phrase site:.gov along with your topic.