There are different laws that apply.
The Constitution (COTUS) is the supreme law of the land. This document establishes our government, and protects certain rights that we are all born with, just because we are human. (This is called "Natural Rights") The only crime specifically mentioned in the COTUS is treason.
The United States Code (USC) is the set of Federal Laws established by Congress, and signed into law by the President (POTUS)
The Code of Federal Regualtions (CFR) is a set of regulations that have the force of law, and are set by agencies with rulemaking powers. The IRS, Postal Service, Parks Service, FDA, Federal Trade Commission, FCC, and FAA are all examples of rulemaking bodies.
As far as how specific laws are applied, more details are needed.

