While federal law applies to all 50 US states, state law is individual. Laws that are put in place in individual states do not apply to other states. This means that it’s possible to do something that is legal in your home state, while the same act could earn you a fine in another state.

Article VI, Paragraph 2 of the U.S. Constitution is commonly referred to as the Supremacy Clause. It establishes that the federal constitution, and federal law generally, take precedence over state laws, and even state constitutions.

When state law and federal law conflict, federal law displaces, or preempts, state law, due to the Supremacy Clause of the Constitution. For example, the Voting Rights Act, an act of Congress, preempts state constitutions, and FDA regulations may preempt state court judgments in cases involving prescription drugs.

The Constitution’s Supremacy Clause provides that federal law is “the supreme Law of the Land” notwithstanding any state law to the contrary. Second, federal law can impliedly preempt state law when Congress’s preemptive intent is implicit in the relevant federal law’s structure and purpose.

The powers not delegated to the United States by the Constitution, nor prohibited by it to the States, are reserved to the States respectively, or to the people.

The Meaning The amendment says that the federal government has only those powers specifically granted by the Constitution. These powers include the power to declare war, to collect taxes, to regulate interstate business activities and others that are listed in the articles.

Bill of Rights – The Really Brief Version