Agencies that typically (although not always) are part of the executive branch can have the authority to create rules and regulations.
Regulations are part of the larger category of administrative law, which also includes executive orders and administrative decisions.
The Federal Register gets updated every weekday and contains all newly proposed regulations as well as revised regulations that were already made available for public comments.
This can be a good resource for finding new regulations or a collection of chronologically ordered regulations.
The Code of Federal Regulations (CFR) receives official updates about once a year.
Unlike the Federal Register, the CFR is organized by subject, making it easier to browse and locate regulations on a similar topic regardless of when they were created.
Westlaw searches the CFR and provides useful annotations that can direct you to relevant cases, law review articles, and more that discuss the regulation in question.