A more thorough explanation:

McCulloch v. Maryland (1819) is a famous court case in the United States that helped define the power of the federal government and its relationship with state governments. The case involved the creation of a federal bank and a tax imposed by the state of Maryland on that bank.

The United States Congress had created the Bank of the United States through a law. The State of Maryland then passed a law that required any bank operating within the state to have a state charter and pay a tax. The state sued McCulloch, who was the cashier of the Baltimore branch of the Bank of the United States, for issuing bank notes without paying the required tax.

The Supreme Court ultimately ruled in favor of McCulloch. Chief Justice John Marshall wrote the opinion for the Court, which had several important conclusions:

• Congress had the power to create the Bank of the United States.
• The Bank of the United States had the right to establish branches within the states, and the states could not tax or interfere with the federal government's exercise of its authority.
• Although the Constitution did not specifically give Congress the power to create a federal bank, Congress had the implied power to do so.
• Congress had wide discretion to make policy decisions as long as those decisions were plainly adapted to a constitutionally authorized end.
• The Supremacy Clause in the Constitution makes federal laws supreme to state laws, and thus prohibits states from enacting laws contrary to federal laws.

Overall, the Court found that the authority to create the bank was implied from Congress's Spending and Taxing power in conjunction with the Necessary and Proper Clause. Additionally, the Supremacy Clause in the Constitution makes federal laws supreme to state laws, and thus prohibits states from enacting laws contrary to federal laws. Consequently, Maryland's tax was unconstitutional.

For example, if the federal government creates a law that says all citizens must wear masks in public during a pandemic, a state cannot pass a law that says its citizens do not have to wear masks. The federal law would be supreme and the state law would be unconstitutional.