What does the Supremacy Clause do?

Makes federal law the highest in the land(apex)

The Supremacy Clause (Article VI, Clause 2) establishes the Constitution as the "supreme law of the land," with which all other laws must comply, and subordinates state statutes to federal statutes and treaties when the two are in conflict.

Article VI, Clause 2:

"This Constitution, and the laws of the United States which shall be made in pursuance thereof; and all treaties made, or which shall be made, under the authority of the United States, shall be the supreme law of the land; and the judges in every state shall be bound thereby, anything in the Constitution or laws of any State to the contrary notwithstanding."